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									                    Report to
            Cornell University Library
      Grant No. 1025-1864 (Prime Agreement)
                      from
         Ford Foundation (Prime Sponsor)




INVESTIGATION OF HERMETIC SEALING
   AS A MEANS OF EXTENDING THE LIFE
        OF FILM-BASED MATERIALS




                   February 28, 2005

                      Prepared by:
         Jean-Louis Bigourdan, research scientist
              Edward Zinn, research scientist
                  James Reilly, director
            Karen Santoro, editorial assistance
               Image Permanence Institute
             Rochester Institute of Technology
Introduction
The Image Permanence Institute at Rochester Institute of Technology, Rochester, New
York was awarded a grant from Cornell University Library to develop a methodology for
minimizing the harmful effect of a hot and humid climate on the life expectancy of film-
based collections. The objective of this research is to develop a simple practical housing
approach for storing silver gelatin polyester-base microfilm for long-term storage. The
investigation focuses on the feasibility of using sealed microenvironments under adverse
climate conditions. The research was designed to (1) evaluate the dimension of the
problem in libraries and archives that are particularly challenged by adverse climate
conditions, such as those found in Southeast Asia and Cuba; (2) develop basic
information on the behavior of polyester-base microfilm when exposed to various
humidity conditions; and (3) establish a procedure for storing polyester-base microforms
for extended periods of time. This report presents the findings of the research and
proposes a practical approach for long-term storage using hermetic sealing techniques.

HERMETIC SEALING METHODS FOR MICROFILM STORAGE
The use of hermetic sealing for film storage is not new; several procedures have been
either suggested or implemented in the past. A number of earlier sources have proposed
the use of desiccants or of moisture conditioning prior to sealing the film materials inside
moisture-proof packages for long-term storage. The aim of both approaches is to control
the amount of moisture left in the film to be stored. Vacuum sealing has also been
implemented to minimize the volume of air inside the final package. These options are
examples of attempts to isolate the film from adverse environmental conditions such as
high RH, which is a critical issue in hot and humid tropical climates. These options are
briefly reviewed and evaluated in the following sections. They have provided the frame-
work for the current research.

Earlier Hermetic Sealing Methods
In the early 1980s, the Swedish Film Institute proposed a methodology for the long-term
storage of color film.1 A film conditioning apparatus (FICA) was conceived and built to
(1) reduce the film moisture content to an acceptable level, and (2) to vacuum seal the
film roll inside a moisture-proof packaging. In this particular application, the sealed
packages were stored at subfreezing temperatures to minimize the risk of chemical decay.
By reducing the film moisture content and placing the film in frozen storage, the stability
of the color dyes and of the cellulose triacetate support were optimized. Although the
primary goal of the procedure was to minimize the chemical decay of otherwise
chemically unstable materials, several principles of the FICA system have value for the
present study. Controlling the microenvironment surrounding the film material is key to
the FICA system. It is achieved by preconditioning the film to low humidity and using
hermetic sealing technology. Particular to the FICA system is the removal of moisture
from the film roll by exposing it to 20°C, 25% RH long enough to achieve moisture

1
 R. Gooes and H.-E. Bloman, “An Inexpensive Method for Preservation and Long-Term Storage of Color Film,”
SMPTE Journal (December 1983): 1314-1316.

                                                                                                            2
equilibrium. This step is controlled by monitoring the weight change of the film roll until
it remains constant at equilibrium with the ambient conditions. Once moisture
equilibrium was achieved, the film roll is vacuum sealed inside two heat-sealable
aluminum-foil bags. This last step has the effect of minimizing extra air inside the bag.
The implementation of the FICA machine resulted in a reduction of the amount of water
contained in the film roll inside the sealed bag. Both the moisture preconditioning step
and the use of the heat-sealable aluminum foil bag for long-term storage have great value
for the present study.

Microclimates Controlled by Desiccants
The use of desiccants (e.g., activated silica gel) to control the moisture content of non-
processed photographic film was investigated more than fifty years ago.2 Although never
widely used, this practice was recommended for the preservation of motion-picture film,
and procedural guidelines were provided to film archivists.3 In 1993, Eastman Kodak Co.
introduced the use of molecular sieves as a way to control the so-called “vinegar
syndrome,” which is a major threat for cellulose-acetate-base collections.4 Although the
interest for such crystalline molecular “cages” using natural or synthetic compounds to
selectively adsorb gaseous components dates back to the 1960s, 5, 6 the ability of
molecular sieves to trap moisture and degradation byproducts from cellulose triacetate
film support prompted a renewed interest in the use of microenvironmental approaches to
film preservation. This development initiated research evaluating the effect of
microenvironments on the chemical stability of acetate-base film. The results of these
studies provided insights into the comparative benefits of managing microclimates and of
controlling the macroclimate. The benefits of using various desiccants (e.g., silica gel and
molecular sieves) inside sealed film containers were quantified.7, 8 Beyond the potential of
this method to minimize further chemical decay, these earlier results are of interest for
this research because they provide basic information on the effectiveness of various
desiccants for the reduction of film moisture content. Results on the effect of molecular
sieves and activated silica gel on 100-ft. 35mm film rolls enclosed in sealed metal cans
have been previously reported.9 The weight loss of the film and the weight gain of the
desiccant provided an insight into the moisture exchange that occurred over time. This
gravimetic monitoring indicated that the moisture adsorption from the film occurred
during the first weeks of storage. These earlier data provided relevant information and
incited further study of the use of desiccants in conjunction with hermetic sealing.


2
  C. J. Kunz and C. E. Ives, “The Use of Desiccants with Undeveloped Photographic Film,” JSMPE 46 (1946): 475.
3
  The Book of Film Care, Eastman Kodak Publication H-23, (Rochester, NY: Eastman Kodak Company, 1983).
4
  A. T. Ram, et al., “The Effects and Prevention of the Vinegar Syndrome,” Journal of Imaging Science and
Technology 38 (1994): 249-261.
5
  D. W. Breck and J. V. Smith, “Molecular Sieves,” Sc. Amer. 200 (1959): 85.
6
  D. W. Breck, “Crystalline Molecular Sieves,” J. Chem. Ed. 41 (1964): 678.
7
  J.-L Bigourdan, P. Z. Adelstein, and J. M. Reilly, “Use of Microenvironments for the Preservation of Cellulose
Triacetate Photographic Film,” Journal of Imaging Science and Technology 42.2, (March/April 1998): 155-162.
8
  J.-L. Bigourdan, “Effectiveness of Storage Conditions in Controlling the Vinegar Syndrome: Preservation Strategies
for Acetate Base Motion-Picture Film Collections,” Image and Sound Archiving and Access: The Challenges of the 3 rd
Millennium, Proceedings to the Joint Technical Symposium Paris 2000, M. Aubert and R. Billeaud, eds., (Paris: CNC,
2000): 14-34.
9
  J.-L. Bigourdan and J. M. Reilly, Environment and Enclosures in Film Preservation, Grant # PS 20802-94, final
report to the Office of Preservation, National Endowment for the Humanities (1997).

                                                                                                                   3
FILM MOISTURE CONTENT

How Critical Is Film Moisture Content?
The importance of environmental conditions in film preservation is well recognized. Heat
and humidity are the primary factors that govern the occurrence and rate of biological
decay, chemical instability, and mechanical damage. Manifestations such as mold
growth, vinegar syndrome, and ferrotyping respectively illustrate these three categories of
decay of photographic film.
High humidity typically promotes mold growth and pest infestation in photographic film
collections. It also provides the moisture that promotes chemical reactions like
hydrolysis. High temperature accelerates the rate of chemical reaction, and it may also
contribute to biological decay and mechanical damage such as ferrotyping or blocking.
These facts underscore the challenges faced by archivists in tropical climates, where hot
and humid conditions are common.
High moisture content in photographic film is caused by the film’s tendency to absorb
moisture from its surrounding environment. This is due mainly, but not exclusively, to
the gelatin binder. Under humid conditions film absorbs moisture; under dry conditions it
desorbs moisture. Both exchanges occur as the film seeks moisture equilibrium with the
surrounding air. Once equilibrium is reached, the film equilibrium moisture content
depends mostly upon the ambient RH. Higher RH causes film to have a higher moisture
content. High moisture content in film provides favorable conditions for ferrotyping or
blocking and makes film more prone to biological decay, chemical deterioration, and
mechanical damage.
The problem of biological decay has been addressed mainly by avoiding high RH levels
in storage areas. Limiting high RH is part of standard recommendations. Today, film
chemical decay is addressed by providing suitable storage environments based on the
relationship between decay rate and temperature and RH conditions.10,11,12 Physical
damage such as ferrotyping or blocking have been addressed by defining allowable
temperature and RH levels to avoid softening of the gelatin binder. Data published by
Mark McCormick Goodhart 13 helped to define safe temperature and RH domains to
minimize the risk of blocking. All of these approaches point to the same fact: film
moisture content must be controlled for long-term film preservation.
Within the framework of this research, which deals with polyester-based black-and-white
microfilm, the challenge is to create a microenvironment for preventing mold growth,
silver oxidation, and ferrotyping or blocking. Earlier studies have indicated that
controlling moisture is the key to achieving this goal. The aim of this study is to define
ways to achieve acceptable moisture-content levels in a variety of situations.



10
   J. M. Reilly, IPI Storage Guide for Acetate Film (Rochester, NY: Image Permanence Institute, 1996).
11
   J. M. Reilly, Storage Guide for Color Photographic Materials (Albany, NY: University of the State of New York,
1998).
12
   P. Z. Adelstein, IPI Media Storage Quick Reference (Rochester, NY: Image Permanence Institute, 2004).
13
   M. H. McCormick-Goodhart, “The Allowable Temperature and Relative Humidity Range for the Safe Use and
Storage of Photographic Materials,” Journal of the Society of Archivists, 17.1 (1996): 7-21.

                                                                                                                    4
Moisture Content Relationships
Temperature, RH, and equilibrium moisture content relationships have been investigated
in previous studies.14 The impact of temperature on the moisture equilibrium curve has
been described in earlier papers, but it has received less attention than has the impact of
RH changes.15,16 In those earlier papers it was recognized that film equilibrium moisture
content was essentially governed by RH. This relationship was re-examined only when
the use of cold storage became a standard recommendation for the preservation of color
and acetate-base photographic materials. It was found that, at constant RH, the moisture
content of 35mm acetate-base motion-picture film is greater at lower temperatures than it
is at higher temperatures. (This behavior is illustrated in Figure 1, which reports data
published in an earlier paper.17) In other words, film in equilibrium at 50% RH contains a
significantly higher weight of water when kept at -16°C (3.6% equilibrium moisture

                                                                    5°C              40°C
                                        4.5              -16°C              20°C
                                                                                             60°C
               Moisture content, wt %




                                         4
                                        3.5
                                         3
                                        2.5
                                         2
                                        1.5
                                         1
                                        0.5
                                         0
                                              0   20     40     60     80
                                                  Relative humidity, %
               Figure 1: Effect of temperature on moisture equilibration curve of 35mm
               color motion picture film on cellulose triacetate base.

content) than it does when kept at 20°C (2.9% equilibrium moisture content). It was
expected, however, that these differences would be small within the common room-
temperature range. The effect of warmer room temperatures (like those encountered in

14
   P. Z. Adelstein, J.-L. Bigourdan, and J. M. Reilly, “Moisture Relationships of Photographic Film,” JAIC 36 (1997):
193-206.
15
   J. M. Calhoun, “Cold Storage of Photographic Film,” Photographic Science and Technique, Section B of PSA
Journal, 18B 3 (1952).
16
   P. Z. Adelstein, C. L. Graham, and L. E. West. “Preservation of Motion-Picture Color Films Having Permanent
Value,” Journal of the SMPTE, 79 (1970): 1011-1018.
17
   J.-L. Bigourdan, P. Z. Adelstein, and J. M. Reilly, “Moisture and Temperature Equilibration: Behavior and Practical
Significance in Photographic Film Preservation,” La Conservation: Une Science en Évolution: Bilan et Perspectives,
Actes Des Troisièmes Journées Internationales d’Études de l’ARSAG (Paris: Association pour la Recherche
Scientifique sur les Arts Graphiques, 1997): 154-164.

                                                                                                                     5
tropical climates) on the moisture equilibration curve was included in the current research
project. Climate assessment conducted during the project indicated that environments
around 80% RH and 30°C are not uncommon storage conditions in tropical climates.
Therefore, knowing the amount of water that film contains at 80% RH, 20°C and at 80%
RH, 30°C, may have great practical significance. Furthermore, knowing how much
moisture must be removed to achieve an acceptable equilibrium moisture content is
important for establishing efficient conditioning procedures.

Moisture Equilibration Rate
IPI developed data on moisture equilibration rate in two previous research projects.
Those studies dealt with a wide range of materials, including film, photographs, paper,
books, and magnetic tape. Each material was investigated in various situations, both in
different types of enclosure and with no enclosure. Both moisture absorption and
moisture desorption were studied by exposing the test samples to either moist or dry
environments at 20°C. Table I reports results for the film materials studied, which have
relevance for the current research. The data indicate that the length of time required to
achieve a given percent equilibration (%E) varies widely depending on film formats and
housing types. To achieve 90% equilibration can be a matter of weeks, months, or years.
These data were obtained by first preconditioning the film to 20°C, 50% RH and then
exposing it to 20°C, 20% RH. This baseline data was used for the current research.
 Table I: Equilibration times determined at 20°C for various film-material/enclosure combinations and film
materials alone when exposed to a one-time RH change from 50% to 20%. Equilibration times are
expressed in days for 50%, 70%, and 90% equilibration.
                                                                 Equilibration Time in Days
                     Test Samples                                   (Moisture Desorption)
                                                             50%            70%           90%
 16mm film roll without enclosure                            1 to 2           3             7
 400′ roll of 16mm motion-picture film in metal can        11 to 18        21 to 23       31 to 33
 100′ roll of 35mm film in cardboard box in metal
                                                            4 to 12          —              —
 cabinet
 35mm film roll without enclosure                           3 to 4         10 to 14       20 to 25
 100′ roll of 35mm film in plastic microfilm box            >200            Year           > Year
 1000′ roll of 35mm film in metal can                      28 to 30          >50          Months
 1000′ roll of 35mm film in vented plastic container          4            10 to 12       28 to 30
 Stack of 175 4″ x 5″ sheet films without enclosure           1               —              —
 Stack of 175 4″ x 5″ sheet films in paper envelopes in
                                                             1 to 2         2 to 3         3 to 9
 cardboard box
 Stack of 175 4″ x 5″ sheet films in paper envelopes in
                                                             5 to 6         11-12           22
 metal cabinet




                                                                                                        6
Research Findings
ASSESSMENT OF THE CURRENT METHOD
The examination of a small number of hermetically sealed samples revealed that the
procedure used for these film materials did not adequately protect them from mechanical
damage. Several years before this project was initiated, these materials were sealed using
heat sealable aluminum foil bags and a vacuum heat sealer. The methodology was
described on March 28, 2001 during a meeting held at the Ford Foundation Headquarters,
New York, NY. Although the approach did minimize the risk for biological decay, such
as mold growth or pest infestation, the procedure induced damaging physical changes in
the silver gelatin layer. Several 16mm microfilm strips enclosed inside polyester jackets
displayed signs of surface changes like ferrotyping. This manifestation of mechanical
decay is typically caused by high humidity and/or high temperature. Previous studies
conducted on photographic materials have indicated that the higher the moisture content
of the gelatin layer, the lower the temperature at which physical changes like ferrotyping
or blocking are likely to occur. The phenomenon occurs at the so-called glass transition
temperature (Tg), which characterizes the point at which the gelatin passes from a “solid-
like” state to a “gel-like” state. In this process, the gelatin binder of photographic film
becomes softer and stickier and can go through surface changes, depending on the
materials with which it is in contact. Contact with a smooth material would give the dull
surface of the film emulsion a shiny appearance (ferrotyping). Soft film emulsion can
also adhere to materials it touches. Film strips stuck to their plastic sleeves and roll film
that cannot be unrolled are typical manifestations of blocking.
Data developed by McCormick-Goodhart (see Table II) indicate the relationship between
water content and Tg for photographic gelatin. Table II shows that the higher the
moisture content is, the lower the Tg value is. Table II also includes the corresponding
equilibrium RH at 21°C. Although these data were obtained by testing unhardened
photographic gelatin, they suggest that when the gelatin is in equilibrium with a high RH
(above 65% at 21°C) it may change state at 30°C or below—common temperatures and
RH levels in tropical climates are given later in this report.
Table II: Moisture properties of photographic gelatin. Data from McCormick-Goodhart.18
            Moisture Content (wt%)                 RH at 21°C (%)                     Tg (°C)
                     11.2                                28                            >80
                     12.0                                44                             64
                        14.4                              57                             40
                        16.6                              66                             28
                        18.2                              73                             16


Such behavior may explain the appearance of the samples sealed under those conditions.
If the sample materials were in equilibrium with a high RH prior to being hermetically

18
  M. H. McCormick-Goodhart, “Moisture Content Isolines and the Glass Transition of Photographic Gelatin: Their
Significance to Cold Storage and Accelerated Aging,” Research Techniques in Photographic Conservation,
Proceedings of the Conference in Copenhagen, 14-19 May 1995.

                                                                                                                 7
packaged, there is a good chance that the gelatin water content was sufficient to promote
the ferrotyping observed on the samples. The data in Table II and examination of the
samples underscore the importance of controlling film moisture content prior to hermetic
packaging for long-term storage. This is more critical if materials are likely to even
momentarily encounter warm temperatures (i.e., 30°C or above). In addition, observation
of the sealed samples cast doubt on the benefit of vacuum sealing for the procedure. The
ferrotyping observed on a small number of the samples examined on March 28, 2001,
suggested that the technique used did not reduce the film moisture content to an
acceptable level.
The examination of these samples did help to articulate the research project and narrow
its main focus. Although the sealing technique used helped to control biological
deterioration, it failed to prevent mechanical damage of the gelatin emulsion. The
vacuum sealing procedure failed to ensure a safe storage microenvironment. Based on
current knowledge, it is believed that controlling the gelatin water content is the most
critical factor in the successful implementation of hermetic sealing for long-term storage
in tropical climates.

DETERMINING OPTIMUM CONDITIONS TO MINIMIZE PHYSICAL
DAMAGE TO THE IMAGE LAYER

Goal
The main objective of this phase was to determine how moisture content, temperature,
pressure, and time relate to physical changes (e.g., ferrotyping or blocking) of the silver
gelatin layer, and to determine the safety zone within which the physical alteration of the
image layer would not be a concern for archivists. The first task was to determine a test
temperature that would promote such defects under real-life humidity conditions. This
was achieved by exposing hermetically sealed film strips having high moisture content to
various temperatures. The second task was to determine how high humidity levels affect
the emulsion surface at given temperatures. This was done by exposing the test samples
to various ambient conditions.

Experimental
Several series of test samples were conditioned to various environments prior to exposure
to direct pressure at different temperatures. Preliminary experiments were conducted to
determine temperature, weight applied, and duration. Two approaches were
simultaneously investigated. In the first, samples inside sealed moisture-proof bags were
exposed to a series of temperatures. In the second, unbagged samples were exposed to a
series of controlled environments. After exposure each strip of film was examined
visually, and the level of damage was evaluated following the criteria included in Table
III. Four levels were chosen to characterize the effect of the test conditions. Evaluation
was based solely on visual examination and focused on determining if the gelatin binder
had, at some point, passed the Tg. The resulting change in the gelatin state would have to
be visually detectable as a change from a rather dull to a glossy surface appearance. The
problem is that this approach remains somewhat subjective, and it still is difficult to
apply consistently. The criteria described in Table III, however, did help to achieve a
useful assessment.

                                                                                             8
Table III: Evaluation criteria used to assess the occurrence and extent of physical damage to the gelatin
layer of 35mm microfilm exposed to a series of environmental conditions.
  Level of Damage                                           Description
      Level 0           No damage observed. Emulsion retains its dull appearance.
                        Few signs of ferrotyping on the edges of the film strip. Emulsion displays a few
        Level 1
                        glossy spots along the strip edges.
                        Extended ferrotyping. Parts of the film strip display a glossy appearance. It may
        Level 2
                        adhere slightly to plastic materials in contact with it.
                        Blocking. Film strips are stuck together throughout the stack. Film adheres to the
        Level 3
                        other material with which it is in contact, such as plastic sleeves.



Effect of Temperature
Each test sample consisted of a stack of ten 35mm microfilm strips. Film strips were
stacked without individual sleeves to maximize the impact of the adverse test conditions.
Each stack was enclosed in a polyester sleeve. Twelve such stacks were prepared and
preconditioned to 21°C, 75% RH. After full equilibration, each stack was wrapped in a
Teflon sheet and heat-sealed inside a moisture-proof aluminum-foil bag. It was believed
that this type of packaging might resemble the final packaging system to be used later, in
the field. Test specimens were then exposed to three different weights. Weight was
distributed over the entire surface of the stack using two flat pieces of glass. Sealed
samples were exposed to 20°C, 40°C, 50°C, 60°C, and 70°C inside a dry oven (Figure 2).
After five weeks of exposure, the samples were examined visually to detect any physical
change in the silver gelatin layer. The samples were examined in order, starting with
those exposed to the highest temperature and working down toward those exposed to the
lowest temperature. Samples kept at 20°C were examined after seven months. Based on
previous studies, it was expected that physical changes might be brought about by these
conditions. The data in Table II suggests that unhardened gelatin may reach glass
transition at a temperature below 20°C.
High temperatures led to major physical changes in the silver gelatin layer of the samples
tested. After five weeks, samples exposed at 40°C, 50°C, 60°C, and 70°C displayed
various degrees of damage. The most drastic changes were obtained at 70°C,
independently of the weight applied. At 70°C, all microfilm strips were blocked together
due to the increased stickiness of the softened gelatin (Figure 3). This behavior was
observed to a lesser degree at lower temperatures, and it was marginal at 40°C after five
weeks of exposure. Ferrotyping at 40°C was marginal and characterized by few glossy
spots on the edges of the film strips. At 60°C the weight applied exacerbated the
phenomenon. Samples kept at 20°C under pressure did not display any damage when
examined after seven months.




                                                                                                             9
Figure 2: Blocking tests conducted inside sealed bags and under various weights at a series of constant
temperatures. Film samples initially conditioned to 21°C, 75% RH.




Figure 3: Test specimen affected by blocking after five weeks at 70°C. Microfilm strips initially conditioned
to 21°C, 75% RH and placed inside heat-sealed aluminum-foil bags under weight.
These results confirm that film materials in equilibrium at 21°C, 75% RH display
physical damage of the gelatin image layer when enclosed inside a sealed bag and
exposed to temperatures of 40°C and above. These observations are consistent with the
data reported in Table II. Table IV indicates that the image layer of samples kept under
pressure at 20°C for seven months did not display any noticeable physical damage. This
suggests that the gelatin did not reach glass transition under these conditions. The
differences between this information and that in Table II can be explained by the fact that
these data were obtained by testing unhardened photographic gelatin.
The study of the effect of temperature leads to the conclusion that a 40°C temperature is
an adequate test condition for the study of the effect of film moisture content on the
physical stability of the gelatin binder. That temperature level promoted noticeable decay

                                                                                                          10
under the lowest test pressure, and periods of 40°C temperatures are not uncommon in
tropical climates.
Table IV: Blocking test results after five weeks of exposure at 40°C, 50°C, 60°C, and 70°C in sealed bags.
35mm Microfilm samples were initially preconditioned to 21°C, 75% RH. Samples kept at 20°C were
examined after seven months.
               Configuration           Temperature (°C)        Weight (kg)       Level of Damage
                                                                   2                     0
                                                20
                                                                   5                     0
                                                                  0.5                    1
                                                40                1.5                    1
        Stack of ten 35mm film                                     5                     1
        strips in polyester sleeve.                               0.5                    1
        Stack enclosed inside a
        sealed moisture-proof                   50                1.5                    1
        package.                                                     5                   1
                                                                    0.5                  1
                                                60
                                                                    1.5                  2
                                                                    0.5                  3
                                                70
                                                                    1.5                  3



Effect of RH at 40°C
A second series of nine test samples was prepared to study the impact of film moisture
content at 40°C. Each test sample consisted of a stack of ten 35mm microfilm strips. The
series was divided into three groups of three sample stacks each. The groups were
conditioned at 40°C to 60%, 70%, and 80% RH, respectively. After full moisture
equilibration each stack was inserted into a plastic sleeve and placed under a weight. Film
strips were stacked without individual sleeves to maximize the impact of the adverse test
conditions. The gelatin image layer of one strip was against the support side of the next
strip. In this experiment, the stacks were not enclosed in a moisture-proof bag so that they
would be exposed to the climate conditions in the chamber. Three temperature- and
humidity-controlled chambers were used for this experiment.
After seven months all film strips were visually examined for damage, such as
ferrotyping and blocking of the gelatin image layer of the film. The visual criteria
described in Table III were used for the evaluation. Results are reported in Table V. The
data indicate that the risk for physical alteration of the gelatin increased as RH was
increased. These data demonstrate that at 40°C and 60% RH or above physical changes
occur after a relatively short time. These observations do not relate directly to Table II,
because temperature alters the moisture equilibrium curve of photographic film (see
Figure 1), but neither do they contradict it. The data reported in Table V confirms that
higher equilibrium RH promotes physical gelatin changes and that pressure may also be a
significant cause of damage under adverse climate conditions.




                                                                                                        11
 Table V: Blocking test results after seven months of exposure at 40°C and 60%, 70%, and 80% RH. Film
strips were first preconditioned to the experiment conditions.
            Configuration           % RH         Approx. Weight (kg)        Level of Damage
                                                         0.5                        1
                                      60                 1.5                        1
                                                          5                         1
                                                          0.5                       2
       Stack of ten 35mm film
                                      70                  1.5                       2
       strips in polyester sleeve
                                                           5                        2
                                                          0.5                       2
                                      80                  1.5                       2
                                                          10                        3



Conclusion
The experiments described above underscored the major impact of temperature and
equilibrium RH in promoting ferrotyping and blocking of the gelatin image layer of
photographic film. Higher moisture content in the film invariably led to gelatin physical
changes at a lower temperature. The data indicate that such damage will occur at 40°C,
60% RH. They also indicate that when film in equilibrium at 21°C, 75% RH is enclosed
in a hermetically sealed package, such physical damage is likely to happen as soon as the
film makes incursions into a 40°C environment (and perhaps an even cooler environment,
as suggested in Table II). While the data in Table II were developed by testing
unhardened photographic gelatin, they do support the idea that lowering the equilibrium
RH to below 50% at 21°C is an efficient way to reduce the water content of the film, and
thereby minimize physical damage to the gelatin layer even at warm temperatures. To
achieve that ultimate goal, two practical approaches were investigated and are described
in the following sections. The first would involve moisture preconditioning the film prior
to hermetic sealing. The second would involve the addition of desiccants along with the
film materials in the moisture-proof packaging. The feasibility of both alternatives is
investigated in the following sections.

MOISTURE EQUILIBRATION RATES

Goal
The objective of this phase of the research is to determine the rate of moisture
equilibration of microfilms exposed to a one-time RH change. The focus is to quantify
the rate of moisture equilibration for materials exposed first to sustained high humidity
and then to a lower humidity level. Exposing test materials to humid conditions for an
extended period simulates a storage scenario common in hot and humid climates. The
challenge is to reduce the material water content to an acceptable level. The water content
level can be determined from Table II, but the means to achieve it in a practical way
remains to be defined. One way is to expose materials having high water content to low-
RH conditions for enough time to enable them to reach a lower, more acceptable water
content. Moisture equilibration rates must be estimated in order to provide adequate

                                                                                                    12
guidelines for this procedure. The major goal of this part of the research is to quantify the
rate of moisture desorption for microfilms exposed to various conditions. Two
consecutive experiments were conducted for this purpose.

Experiment 1
Microfilm roll samples were prepared and moisture-preconditioned at several humidity
levels prior to exposure to a one-time humidity change. The rate of moisture equilibration
was then monitored. For this part of the study, 16mm and 35mm black-and-white
polyester-base microfilms were used. For each film format, a series of 100-ft. rolls was
prepared using the same winding tension. Samples were moisture-preconditioned to three
different RH levels: 50% RH (moderate), 75% RH (high), and 90% RH (high).
Preconditioning temperatures and humidity levels are given in Table VI. These
conditions were selected to represent those typically encountered in tropical regions,
within the range of capability of the equipment used for this study. The data developed
previously in this project helped to inform these decisions. All samples were exposed
until they reached full moisture equilibration. Full moisture equilibration was determined
gravimetrically by weighing each sample over time. Once moisture equilibration was
completed, all samples were ready for the next step of the study.
After moisture preconditioning, all samples were placed into a new environment
maintained at 25°C, 20% RH. The objective of this part of the study was to determine the
rate of moisture equilibration of film when it is exposed to lower RH. This information
was critical for the project, because it provided information on the minimum equilibration
time required to lower the moisture content of film that had been exposed to high
humidity to a safe level. These data were essential to the achievement of the project’s
goals.
All film samples were placed on a solid surface and kept at 25°C, 20% RH during the
entire experiment. The rate of moisture desorption was monitored by weighing the
samples over time, a method used in previous IPI studies.
Figure 4 illustrates the weight change of a 16mm microfilm monitored for a 30-day
period. Sample A was preconditioned to 21°C, 75% RH and then conditioned to 25°C,
20% RH. The weight of the sample was recorded over time for as long as change
continued to occur. Using the same data set, Figure 5 illustrates the rate of equilibration
as %E. The initial weight of the sample in equilibrium with the initial conditions (21°C,
75% RH) corresponds to 0% equilibration. The weight of the sample in equilibrium with
the chamber conditions (25°C, 20% RH) corresponds to 100% equilibration. In the past,
this type of data analysis has been effective in comparing rates of equilibration obtained
by using various RH differentials.19 Figure 5 indicates that it took about one day for
sample A to reach 50% equilibration and about six days to reach 90% equilibration.
Table VI describes the testing situation and summarizes the results obtained for 16mm
microfilms. Table VI and Figure 6 compare the equilibration times for 16mm film rolls
(samples A, D, and I) conditioned on a solid surface inside a climate-controlled chamber.
The results show that full equilibration may require over ten days for each 16mm roll

19
     Bigourdan and Reilly, Environment and Enclosures.

                                                                                           13
regardless of the temperature and RH used for moisture preconditioning. The data
indicate, however, that the different preconditioning RH levels do produce somewhat
different equilibration curves.
Excluding the results obtained for sample D, which was preconditioned at an extremely
high RH, Figure 6 shows that the equilibration rates for samples A and I were similar
despite their different preconditioning temperature and RH. Differences of this nature
were observed when moisture-adsorption rates of 35mm motion-picture film rolls were
tested in an earlier study.20

Table VI: Equilibration times for 16mm microfilm rolls exposed to various climate conditions. All test
samples were placed on a solid surface during equilibration.

                                               Initial        Type of                  Time to Reach %E (Days)
     Sample
                                             Conditions        Reel          50%              70%        90%      100%
        A                                  21°C, 75% RH         3             1                 2         6      About 15
        D                                  30°C, 90% RH         3             2                 4         11     15 to 20
        I                                  30°C, 50% RH         3            <1               <2            5    About 15



                                            0



                                         -0.05
              Weight change (in grams)




                                          -0.1



                                         -0.15



                                          -0.2



                                         -0.25



                                          -0.3
                                                 0        5             10        15         20        25        30
                                                                              Days


Figure 4: Moisture equilibration for 100-ft. 16mm microfilm roll (sample A) exposed without enclosure.
Film initially conditioned to 21°C, 75% RH and kept at 25°C, 20% RH. Weight change in grams versus
time.




20
     Bigourdan and Reilly, Environment and Enclosures.

                                                                                                                        14
           100

           90

           80

           70

           60
      %E




           50

           40

           30

           20

           10

            0
                 0                 5           10            15           20             25            30
                                                            Days

Figure 5: Moisture equilibration for 16mm 100-ft. microfilm roll (sample A) exposed without enclosure.
Film initially conditioned to 21°C, 75% RH and kept at 25°C, 20% RH. Percent equilibration versus time.


                      100

                          90

                          80

                          70

                          60
                     %E
                          50                                              Sample A

                          40                                              Sample D

                          30                                              Sample I

                          20

                          10

                          0
                               0       1   2        3   4         5   6        7     8        9   10
                                                             Days

 Figure 6: Moisture equilibration for 100-ft.16mm microfilm rolls exposed without enclosure to 25°C, 20%
RH. Sample A initially conditioned to 21°C, 75% RH. Sample D initially conditioned to 30°C, 90% RH.
Sample I initially conditioned to 30°C, 50% RH. Percent equilibration versus time.


Four other 100-ft. 35mm microfilm rolls were preconditioned to a variety of
environments as indicated in Table VII. This approach produced different levels of
moisture content in the films, depending on their preconditioning RH levels. All samples
were then placed on a solid surface and exposed to the same environment (25°C, 20%

                                                                                                            15
RH). In this case, however, it should be noted that the films were wound on three
different reel types, as illustrated in Figures 7 to 9. Samples E and F were preconditioned
to 30°C, 90% RH. However, their equilibration rates were significantly different. The
slowest rate, observed in sample E, illustrates the effect of reel type 1, which has solid
flanges that prevented moisture diffusion. In comparison, reel type 2 used for sample F
sped moisture equilibration by facilitating moisture diffusion. Reel type 3, with open
flanges, allowed for even faster moisture equilibration. Test results are reported in Table
VII and Figure 10. The data indicate that, for all samples, full equilibration would require
one month or more depending on the temperature and RH used for moisture
preconditioning and on the type of film reel.
Table VII: Equilibration times for 35mm microfilm rolls initially exposed to various climate conditions and
then placed in a 25°C, 20% RH environment.

                          Initial         Reel               Time to Reach %E (Days)
          Sample
                        Conditions        Type        50%         70%         90%         100%
             B        21°C, 75% RH          1          10          20          40
             E        30°C, 90% RH          1          12          25          45
             F        30°C, 90% RH          2           5         <12          24
             G        30°C, 50% RH          3          <4           7         <17          >30




Figure 7: Film roll on reel type 1   Figure 8: Film roll on reel type 2     Figure 9: Film roll on reel type 3
(sample E).                          (sample F).                            (sample G).




                                                                                                        16
      100

       90

       80

       70

       60
                                                                     Sample B
 %E




       50
                                                                     Sample E
       40                                                            Sample F

       30                                                            Sample G

       20

       10

       0
            0      5         10        15        20        25        30         35        40
                                                Days

Figure 10: Moisture equilibration for 100-ft. 35mm microfilm rolls exposed without enclosure to 25°C,
20% RH. Sample B initially conditioned to 21°C, 75% RH. Samples E and F initially conditioned to 30°C,
90% RH. Sample G initially conditioned to 30°C, 50% RH. Percent equilibration versus time.



Impact of Film Reel Design
Results obtained with samples E and F indicate that the film reel design may have a
significant impact on the rate of moisture equilibration Samples E and F were wound on
reels of two different types. Based on reel design, it was expected that sample F (see
Figure 8) might benefit from a faster rate of moisture equilibration than sample E (see
Figure 7). Although both film rolls were preconditioned to the same environment, Figure
11 illustrates a noticeable difference in equilibration rate. It took roughly twice as long
for sample F to reach given percents of equilibration as it took sample E. The solid sides
of the sample F reel slowed the moisture equilibration of the film.




                                                                                                    17
          100

           90

           80

           70

           60
     %E




           50                                                             Sample E

           40
                                                                          Sample F
           30

           20

           10

           0
                0      5         10        15        20         25        30         35        40
                                                    Days

Figure 11: Moisture equilibration for 100-ft. 35mm microfilm rolls exposed without enclosure to 25°C,
20% RH. Samples initially conditioned to 30°C, 90% RH. Sample E was wound on a film reel with solid
sides. Sample F was wound on a reel with open sides.

Impact of Microfilm Format
The data developed during this experiment help to quantify the impact of microfilm
width on the rate of moisture equilibration. Figure 12 compares 16mm and 35mm
microfilm rolls and shows that the wider the microfilm is, the slower moisture
equilibration is. While a 16mm microfilm roll is fully equilibrated after about two weeks,
a 35mm microfilm roll requires about four weeks. There are even greater differences in
percent equilibration. According to Figure 12, the 16mm microfilm roll reached 50% E
after one day, while it took the 35 mm microfilm roll more than three days to reach the
same point. Assuming that it would require no more than half the time for 16mm than for
35 mm would be a safe prediction based upon the empirical data.




                                                                                                        18
          100

           90

           80

           70

           60                                                         Sample I
     %E




           50                                                         Sample G

           40

           30

           20

           10

           0
                0      5         10        15         20        25        30         35        40
                                                    Days

Figure 12: Moisture equilibration for 100-ft. 16mm microfilm roll (sample I) and for100-ft. 35mm
microfilm roll (sample G). Both rolls were wound on the same type of reel and exposed without enclosure.
Film initially conditioned to 30°C, 50% RH and kept at 25°C, 20% RH. Percent equilibration versus time.

Combined Effects of Film Width and Reel Design
The data developed in Experiment 1 indicate that the width of the film and the design of
the film reel have a significant impact on the rate of moisture equilibration to a lower RH
level. Together, film width and reel design can have an even greater impact, as shown in
Figure 13. These data illustrate the decreased moisture equilibration rate for a wider film
wound on a reel with solid flanges (type 1). Sample A, a 100-ft. 16mm film roll on an
open reel (e.g., type 3), reaches 90% equilibration after six days, while sample B, a
35mm 100-ft. film roll on a solid-sided reel (type 1) requires about 40 days to reach the
same %E.




                                                                                                      19
           100

           90

           80

           70

           60
      %E




           50                                                            Sample B

           40                                                            Sample A
           30

           20

           10

            0
                 0      5         10         15        20         25        30         35         40
                                                      Days

Figure 13: Moisture equilibration for 100-ft. 16mm microfilm roll (sample A) and for 100-ft. 35mm.
microfilm roll (sample B). Sample A was wound on an open plastic reel (see Figure 3). Sample B was
wound on a reel with solid flanges (see Figure 2). Both rolls exposed without enclosure. Film initially
conditioned to 21°C, 75% RH and kept at 25°C, 20% RH. Percent equilibration versus time.


This first experiment brought to light the number of parameters that govern the rate of
moisture equilibration. Film width and film reel design significantly alter the rate of
moisture equilibration. It was also observed that RH differential may have a noticeable
impact when film was exposed to extremely high RH (e.g., 90% RH) under these adverse
conditions. The higher film moisture content is, the longer it takes film to reach
equilibrium with low RH conditions.

Experiment 2
The procedure described above was repeated on a wider range of photographic film
formats, using several housing configurations. The film formats and sample
configurations tested are listed in Table VIII. In this experiment 100-ft.35mm and 16mm
microfilm rolls were tested simultaneously inside typical cardboard microfilm boxes and
without enclosures. Stacks of 4 x 5-inch sheet film were also tested in several housing
configurations (without enclosure, inside individual polyester sleeves, and inside
individual paper envelopes). Although the 4 x 5-inch format is not a microfilm format, it
was included to explore the behavior of flat photographic film. Film and enclosures were
moisture-preconditioned at high humidity at 20°C, 80% RH in a temperature- and
humidity-controlled walk-in chamber for a period of five weeks. After moisture
preconditioning, the test samples were assembled and exposed to low humidity at 20°C,
30% RH until they reach full moisture equilibration. The process was monitored
gravimetrically by weighing each test sample over time. The data were analyzed using
the methodology described in the previous experiment. The evaluation of the
equilibration rate was translated into %E over time. The initial weight of the sample
                                                                                                          20
conditioned to 20°C, 80% RH corresponds to 0% equilibration. The final weight of the
sample conditioned to 20°C, 30% RH corresponds to 100% equilibration.
Table VIII: Equilibration times for film materials in various housing configurations initially conditioned to
20°C, 80% RH and then placed in a 20°C, 30% RH environment.

            Film          Sample               Reel                         Time to Reach %E (Days)
Sample                                                    Container
           Format       Configuration          Type                      50%     70%      90%    100%
                         100-ft. roll on                                                  About
   L        35mm                                 1          None          10       24            >>40
                            solid reel                                                     40
                         100-ft. roll on
   M        35mm                                 3          None           6         16       >40       >>40
                            open reel
                         100-ft. roll on                  Cardboard
   N        35mm                                 1                         2         12       >40       >>40
                            solid reel                       box
                         100-ft. roll on
   O        16mm                                 3          None          1.5        4         13        >20
                            open reel
                         100-ft. roll on                  Cardboard
   P        16mm                                 3                         1         2          6        >20
                            open reel                        box
                           Stack of 25
                       polyester jackets
   Q        16mm       each containing 5        —           None          0.5        1          3        >25
                        strips of 16mm
                            microfilm
                       Stack of 25 sheets
   R        4" x 5"       in individual         —           None          <1         2          6        >25
                        paper envelopes
                       Stack of 25 sheets
   S        4" x 5"       in individual         —           None          1.5        4         12        >30
                       polyester sleeves



Impact of Film Reel Design
Results illustrated in Figure 14 compare the rate of moisture equilibration from 80% to
30% RH at 20°C for 35mm microfilms wound on two types of plastic reel. Results
confirm that the reel with solid sides (sample L) tended to slow down the moisture
desorption process as compared to the open reel (sample M). This difference is
particularly significant during the first part of moisture equilibration. It is worth noting
that reel design alters the rate of moisture equilibration by either promoting or preventing
moisture diffusion.




                                                                                                          21
           100

            90

            80

            70

            60
                                                                               Sample L: 35mm on
      %E




            50
                                                                               solid reel
            40                                                                 Sample M: 35mm
                                                                               on open reel
            30

            20

            10

            0
                 0      5        10        15       20        25        30
                                         Days

Figure 14: Moisture equilibration for two 100-ft. 35mm rolls from 80% to 30% RH at 20°C. Sample L was
wound on a reel with solid sides (type 1). Sample M was wound on a reel with open sides (type 3). Percent
equilibration versus time.

Impact of Microfilm Enclosure
Earlier studies have demonstrated that enclosure material and design have a great impact
on the moisture equilibration rate of roll film. Cardboard is a porous material through
which moisture can diffuse easily. Plastic, such as polypropylene, when associated with a
tight design, can produce a semipermeable environment for microfilms. IPI has
developed data indicating that moisture equilibration within an enclosure can be strongly
governed by the enclosure’s design. In porous enclosures, it is the film roll that primarily
determines the rate of moisture equilibration; the role of the enclosure usually is
marginal. In a plastic microfilm box, the rate of equilibration is controlled by the
enclosure, and the time required for full equilibration can be very long. Such behaviors
are shown in Figure 15, where data obtained in an earlier study at 21°C illustrate the
effects of various enclosures on the rate of moisture adsorption for photographic film.
Figure 15 indicates that film kept inside a plastic microfilm box would require an
impractical length of time to equilibrate to a new ambient RH and that equilibration can
be much faster when film is kept in a cardboard box.
In some circumstances, it may be more practical to keep film rolls inside their containers
during equilibration. To investigate the consequences of this approach, moisture
desorption rates for two samples, sample L with no enclosure and sample N in a
cardboard box, were compared. Both 100-ft. 35mm microfilm rolls were first conditioned
to 20°C, 80% RH and then exposed to a steady 20°C, 30% RH environment. The
equilibration process was monitored by weighing the two samples. The resulting
equilibration curves are plotted in Figure 16. The data appear to indicate a faster rate of

                                                                                                       22
moisture desorption for sample N, especially during the first part of the process. This
result can be explained by the fact that the box equilibrates faster than the film and that at
the beginning of equilibration most of the moisture change is occurring in the box. In
fact, there is no reason why the film should equilibrate faster when it is exposed inside a
cardboard box. If anything, it should equilibrate more slowly. The important observation
here is that the cardboard box did not prevent moisture equilibration at all, and that
keeping materials in their cardboard enclosures during equilibration will not slow the
process. (However, materials should be removed from plastic boxes to facilitate
equilibration.) Figure 17 illustrates similar results for 16mm film rolls.




Figure 15: Rates of moisture equilibration for 100-ft. 35mm film rolls in various enclosures. Percent
equilibration versus time.




                                                                                                        23
             100

              90

              80

              70

              60
                                                                                      Sample L: 35mm
         %E                                                                           on solid reel
              50

              40                                                                      Sample N: 35mm
                                                                                      on solid reel in
              30                                                                      cardboard box

              20

              10

               0
                   0        5     10          15        20        25        30
                                          Days
Figure 16: Moisture equilibration for two 100-ft. 35mm microfilm rolls from 80% to 30% RH at 20°C.
Both film rolls were on reels with solid sides (type 1). Sample L was exposed without enclosure. Sample N
was enclosed inside a cardboard microfilm box during equilibration. Percent equilibration versus time.

             100

              90

              80

              70

              60                                                                 Sample O: 16mm on open
                                                                                 reel
        %E




              50
                                                                                 Sample P: 16mm on open
              40                                                                 reel inside cardboard box

              30

              20

              10

               0
                   0    5       10       15        20        25        30
                                        Days


Figure 17: Moisture equilibration for two 100-ft. 16mm microfilm rolls from 80% to 30% RH at 20°C.
Both film rolls were on reels with open sides (type 3). Sample O was exposed without enclosure. Sample P
was enclosed inside a cardboard microfilm box during equilibration. Percent equilibration versus time.




                                                                                                             24
Effect of Film Width
Figure 18 compares the behavior of 16mm and 35mm microfilm. Both film formats were
tested in the form of 100-ft. rolls wound on the same type of open plastic reel. Both test
samples were exposed to the same RH differential at 20°C. The difference observed in
Figure 18 results from the difference in the width of the microfilms. As observed in the
previous experiment, the data here show that a roll of 35mm microfilm requires
significantly more equilibration time than a roll of 16mm microfilm. The 16mm film
reached 70% equilibration in only a few days; the 35mm film took over two weeks to
reach that point. To conclude, any moisture-conditioning procedure must take into
account the width of the film to be treated.



      100

       90

       80

       70

       60
                                                                            Sample M: 35mm
 %E




       50                                                                   on open reel

       40                                                                   Sample O: 16mm
                                                                            on open reel
       30

       20

       10

       0
            0     5        10        15       20        25       30
                                    Days

Figure 18: Moisture equilibration for 100-ft. rolls of 16mm and 35mm film from 80% to 30% RH at 20°C.
Both film rolls were on reels with open sides (type 3) and were exposed to the new environment without
enclosures. Percent equilibration versus time.

Impact of Film Format
The rate of moisture equilibration for film stacks was also investigated in Experiment 2.
Stacks of 25 units were prepared, first by moisture-conditioning all materials at 20°C,
80% RH. Sheet films, 16mm microfilm strips, paper envelopes, polyester sleeves, and
polyester microfilm jackets were exposed during the same period to achieve full moisture
equilibration. The test samples were then assembled and exposed to a new environment at
20°C, 30% RH. Sample Q consisted of a stack of 25 16mm microfilm jackets (each
containing five film strips). Sample R consisted of a stack of 25 4 x 5-inch sheet films
inside individual paper envelopes. Sample S consisted of a stack of 25 4 x 5-inch sheet
films inside individual polyester sleeves. Figure 19 illustrates the rate of moisture

                                                                                                    25
conditioning for all three samples. Although the data indicate significant differences in
during the moisture-conditioning process, the differences are small at the end of the
process. Depending on sample configuration, it took three, six or 12 days to reach 90%
equilibration. However, 100% equilibration required several weeks for all samples.

          100

          90

          80

          70
                                                                             Sample R: stack of 4x5 in
                                                                             paper envelopes
          60
                                                                             Sample S: stack of 4x5 in
     %E




          50                                                                 polyester sleeves

          40                                                                 Sample Q: 16mm jackets
                                                                             stack
          30

          20

          10

           0
                0    5         10        15       20        25        30
                                       Days


Figure 19: Moisture equilibration for 16mm microfilm strips and 4 x 5-inch sheet films from 80% to 30%
RH at 20°C. Both film formats were exposed as 25-unit stacks. Microfilm strips were inserted inside plastic
jackets, and sheet films were enclosed inside individual enclosures (paper envelopes and polyester sleeves
were tested). Percent equilibration versus time.

Conclusion
The rate of moisture equilibration can be altered by a number of variables. In the two
experiments described above, the moisture equilibration rate of the test samples was
highly dependent on their formats (rolls versus stacks), film width, film reel design, and
housing. The data show greater differences among formats during the equilibration
process, at a given %E, than at full equilibration. As a means of reducing the moisture
content of microfilm, full equilibration may require an impractical length of time: more
than one month under the most unfavorable circumstances. Depending on the RH level
maintained in the conditioning space, however, full equilibration may not be needed to
achieve an acceptable film moisture content, and this is the key to making conditioning a
practical procedure for archivists. If low RH conditions are maintained in the
acclimatization space, the length of conditioning time can be reduced significantly.
Reaching hygrometric half-life (i.e., the time required to achieve 50% moisture
equilibration) can be sufficient, without compromising the goal of an acceptable film
moisture content. Tables VI to VIII suggest that 50% equilibration could be reached in a
matter of days or weeks. To compare, 16mm microfilm rolls and film stacks equilibrated
to 50%E rapidly, and 35mm microfilm rolls equilibrated to 50%E slowly. These data


                                                                                                         26
help to define a moisture-conditioning procedure that would be practical for use in a
variety of situations.

MOISTURE CONDITIONING PRIOR TO PACKAGING—OUTLINE OF
PRINCIPLES AND PROCEDURES
The data developed during this research demonstrate that it is possible to condition
microfilm materials to low equilibrium RH within a reasonable time frame. It is believed
that it is a relevant approach to the problem addressed in this study and that it would
provide a suitable alternative to the desiccant method. The experiments described above
indicated that film in equilibrium with high RH can be conditioned to lower RH within
days or weeks, depending on the circumstances. This method requires the availability of
an area in which microfilms could be prepared for long-term storage. The first step is to
condition the film in terms of moisture content. The second step is to hermetically
package the film.

Film Moisture Conditioning
In order to establish the procedure, the following three questions must be answered: What
is the initial moisture content of the film? What would an acceptable moisture content be?
And finally, in what type of environment and for how long should the film be
conditioned?

Initial Equilibrium RH
Given the temperature and RH data gathered from several institutions located in tropical
climates it is likely that, after processing and subsequent storage, films kept in these
locations will have a high water content. Observations made during this research
indicated that the water content of films in some institutions is high enough to promote
damage of the gelatin layer. In fact, humidity as high as 80% RH at normal room
temperature is commonly encountered. The prevalence of such conditions is a convincing
argument for conditioning films before hermetic packaging. Figure 1 indicates that at
20°C, 80% RH, acetate-based motion picture film may contain about 4 weight percent
(wt %) of water. Data presented later in this report indicates that 35mm polyester-based
microfilm contains a similar amount of water at these conditions.

Acceptable Equilibrium RH
The data reported in Table II indicate that unhardened photographic gelatin would not
suffer physical damage below 64°C when its water content corresponds to equilibrium at
21°C, 44% RH. Figure 1 indicates that under these climate conditions film may contain
about 2.5 wt % of water. The data developed in this research confirm these earlier
determinations. This data and observations made during the blocking tests suggest that
conditioning to an equilibrium RH of 45% or below at room temperature would be a
reasonable goal. These conditions would minimize the risk of physical damage caused by
ferrotyping or blocking. In addition, the moderate or low RH would insure that the silver
image, which contains the microfilm information, would not be subject to oxidation.




                                                                                        27
Moisture-Conditioning RH
To achieve an acceptable moisture content level, film materials should be conditioned
until they reach an equilibrium RH of, at most, 45% at normal room temperature. To
reach this goal, archivists can choose from several appropriate acclimatization
environments. For instance, the conditioning space could be maintained at 20°C, 45%
RH, or at dryer conditions such as 20°C, 30% RH. Such a difference in RH would
influence the choice of conditioning procedure. While the former would require full
moisture equilibration, the latter would not, making it possible to reduce conditioning
time and yet provide the same level of protection for the film. Since the RH differential
does not significantly alter the rate of moisture equilibration, the dryer the conditioning
space is, the shorter the equilibration time will be. In practice, archivists will need a
conditioning space at 20°C with 45% RH or lower. Once the acclimatization environment
is known, the minimum time for conditioning can be determined.

Minimum Moisture-Conditioning Time
To clarify this approach it might be helpful to re-examine the data developed for one 100-
ft. 35mm microfilm roll (sample L) and for one stack of 4 x 5-inch film sheets (sample
S). Sample L was characterized by a hygrometric half-life of ten days and the slowest
equilibration rate found at 20°C. Sample S had a hygrometric half-life of less than two
days, which is characteristic of faster equilibrating flat film formats (see Table VIII). The
rates of conditioning from 80% to 30% RH evaluated at 20°C for sample L and sample S
provide baselines for determining the minimum time required to reach an equilibrium RH
of 45% at 20°C.
Table IX translates the 45% RH target into %E based on the initial equilibrium RH and
the RH maintained inside the conditioning room. It is assumed that the initial equilibrium
RH of the areas in which microfilms are likely to be stored may vary from 50% to 80%
RH. Data gathered from several institutions demonstrated that such high RH levels may
be encountered in tropical regions. While an environment at 50% RH does not present
any significant risk, an environment at sustained higher RH increases the risk of physical
damage to the gelatin layer. The conditioning RH values included in Table IX represent
the archivist’s options. The conditioning RH may vary from one institution to another,
depending on the available space, the dehumidification equipment used, the investment
made by the institution, and, above all, the local climate. Nevertheless, the procedure will
require a conditioning RH of 45% or below at room temperature. The %E values defined
in Table IX can be used as guidelines to determine minimum conditioning times for a
range of real-life situations. The %E values indicate that the lower the RH in the
conditioning space is, the lower the required %E is. The key is to transform these values
into actual times, such as number of days, as in Figure 20, which shows the relationship
of %E and time. Tables X and XI are directly related to Table IX and Figure 20. For
every %E in Table IX there is a corresponding number of days. Likewise, for every
environmental situation there is a corresponding minimum conditioning time.
Tables X and XI contain all the information archivists need to carry out the moisture-
conditioning procedure on 35mm roll film and stacks of flat films. Depending on the
initial equilibrium RH and on the conditioning RH, film materials may have to sit from a
half day to more than one month before they are packaged. However, the data indicate

                                                                                          28
that maintaining the conditioning room RH at 30% or below would mean that fast
equilibrating configurations like sheet-film stacks would need less than one week to
equilibrate to 45%E, even when the film was initially in equilibrium with extremely high
humidity, such as 90% RH. Under similar high-humidity conditions slow equilibrating
film configurations would need about a month for moisture conditioning. If archivists can
only maintain 40% RH in the acclimatization room, they could refer to Tables X and XI
to determine the shortest moisture equilibration time for that condition. It should be noted
that choosing this option would mean that conditioning slow equilibrating formats like
35mm microfilm rolls would take well over one month, and that could result in material
workflow problems.
Table IX: Relationship between equilibrium RH, conditioning RH, and %E corresponding to an
equilibrium RH of 45% at 20°C.
                                        %E Required to Achieve a 45% Equilibrium RH Based on RH in
                                                        Conditioning Space at 20°C
                                         20% RH          30% RH         40% RH          45% RH
                        50%                 17              25              50             100
   Initial              60%                 38              50              75             100
 Equilibrium
 RH at 20°C             70%                 50              63              83             100
                        80%                 58              70              88             100
                        90%                 64              75              90             100




           100

            90

            80

            70

            60
      %E




            50                                                                      Sample L: 35mm on
                                                                                    solid reel
            40
                                                                                    Sample S: stack of
            30
                                                                                    4x5 in polyester
                                                                                    sleeves
            20

            10

            0
                 0       5         10        15         20        25        30
                                            Days

Figure 20: Moisture equilibration for film from 80% to 30% RH at 20°C. Sample L: is a 100-ft. 35mm
microfilm roll on reel with solid sides (type 1). Sample S is a stack of 25 sheet films (4 x 5-in.) enclosed in
individual polyester sleeves. Percent equilibration versus time.


                                                                                                              29
Table X: Moisture conditioning of 100-ft. 35mm microfilm roll. Minimum conditioning times to achieve an
equilibrium RH of 45% at 20°C, based on the initial equilibrium RH and on the RH maintained inside the
conditioning space.
                              Minimum Equilibration Time to Achieve an Equilibrium RH of 45%,
                                Based on RH Maintained in Conditioning Space at 20°C (Days)
                                 20% RH             30% RH           40% RH          45% RH
                  50%               1                   2               10             >30
   Initial        60%               5                  10               30             >30
 Equilibrium      70%               10                 17              >30             >30
 RH at 20°C       80%               15                 24              >30             >30
                  90%               20                 30              >30             >30



Table XI: Moisture conditioning of 25-sheet film stack. Minimum conditioning times to achieve an
equilibrium RH of 45% at 20°C, based on the initial equilibrium RH and on the RH maintained inside the
conditioning space.
                              Minimum Equilibration Time to Achieve an Equilibrium RH of 45%,
                                Based on RH Maintained in Conditioning Space at 20°C (Days)
                                 20% RH             30% RH           40% RH          45% RH
                  50%              0.5                 0.5              1.5            >30
   Initial        60%               1                  1.5               5             >30
 Equilibrium      70%              1.5                  3                8             >30
 RH at 20°C       80%               2                   4               10             >30
                  90%               3                   5               13             >30



MOISTURE CONTENT, TEMPERATURE, AND RH RELATIONSHIPS

Goal
The objective of this part of the research was to evaluate the impact of temperature and
RH on the equilibrium moisture content of photographic film. Previous film studies
conducted on triacetate-base motion-picture film demonstrated that temperature can alter
the direct relationship between RH and film moisture content. These studies concluded
that both temperature and RH determine the amount of water that film holds at
equilibrium. In the context of this research project, that information is essential in order
to know (1) how much water microfilms hold at a common temperature and at various
RH conditions and (2) what amount of water, if any, must be removed from the films
prior to hermetically packaging them for long-term storage.

Experimental
This part of the study was conducted on 35mm microfilm, microfiche, and 4 x 5-inch
sheet film. All film formats were on polyester support. The experimental procedure
described here varies from the one initially planned and described in the interim report on
the research. It is believed that the chosen experimental procedure more accurately
reflects real-life situations.


                                                                                                     30
Test environments were created at two temperatures, 20°C and 30°C, and at five different
RH levels: 11%, 47%, 60%, 70%, and 80%. First, film samples were fully equilibrated to
the five humidity levels at 20°C and then weighed. The same samples were then
equilibrated to the same five humidity levels at 30°C and weighed again. The moisture
content was determined by thermo-gravimetric analysis. Based on preliminary testing, the
following procedure was used: The samples were dried at 120°C for two hours. Weights
were determined after the samples had cooled to 20°C. This method provided an
evaluation of the impact of RH on the film moisture content at 20°C and 30°C.

Results
The data reported in Figure 21 shows that film moisture content is strongly dependent
upon RH conditions. The results also indicate that common ambient temperatures alter
the moisture equilibrium curves. Film conditioned to 80% RH contains more moisture at
20°C than at 30°C. Similar behavior is illustrated in Figure 1 for acetate-based motion-
picture film. Results of the current research indicate that the moisture content of
polyester-based microfilm tends to be slightly lower than the moisture content of acetate-
based motion-picture film in a given environment. At 20°C, 80% RH, the polyester-based
microfilm contains about 0.25 wt. % less water than the acetate-based motion-picture
film.
Figure 21 unveils significant differences between 35mm microfilm and microfiche. The
amount of moisture that each type of film retains varies widely. At 20°C, 80% RH,
moisture content values vary from 4.5 wt % for 35mm microfilm to less than 1 wt % for
the microfiche samples. While these behaviors don’t have any implications regarding the
implementation of the conditioning method, they add to our understanding of the
mechanisms involved in the desiccant method. According to the moisture equilibrium
curves plotted in Figure 21, it is expected that much more water will have to be removed
from one hundred grams of 35mm microfilm than from microfiches weighing the same
amount. These differences in moisture content are illustrated in Figure 22, which shows
the weight of water contained in one 100-ft. 35mm microfilm roll (i.e., about 200 grams
of film) and in a stack of 100 microfiches (i.e., about 400 grams of film). It can be
concluded from these data that, to achieve an equilibrium RH of 45% at 20°C, materials
initially in equilibrium with higher RH will have to lose a specific amount of water. A
100-ft. 35mm microfilm roll conditioned to 20°C, 80% RH would have to desorb about
three grams of water to reach an equilibrium RH of 50% RH. For the same RH
differential, a stack of 100 microfiches would have to desorb one gram of water. If the
moisture-conditioning method is used, the time required for the moisture content change
will depend only on the type of film and not on the RH differential. Use of the desiccant
method will require the adjustment of the amount of moisture adsorbents used based on
the RH differential. That aspect is addressed in the following sections.




                                                                                       31
              5.0

                                                                    microfiches at 20°C
              4.5
                                                                    microfiches at 30°C

              4.0
                                                                    4x5 film 20°C


              3.5                                                   4x5 film 30°C

                                                                    35mm at 20°C
              3.0
                                                                    35mm at 30°C
      % EMC




              2.5


              2.0


              1.5


              1.0


              0.5


              0.0
                    0                                               10              20     30         40          50         60     70    80   90
                                                                                                           % RH


Figure 21: Equilibrium moisture content data obtained for 35mm microfilm, microfiches, and 4 x 5-inch
film sheets at 20°C and 30°C.

                                                                9

                                                                            35mm 100-ft. microfilm
                                                                8           roll without enclosure
                    Amount of water in test sample (in grams)




                                                                            stack of 100 microfiches
                                                                7           without enclosure

                                                                6


                                                                5


                                                                4


                                                                3


                                                                2


                                                                1


                                                                0
                                                                     20%             30%        50%        60%         70%        80%    90%
                                                                                                           RH

Figure 22: Estimates of the amount of water contained in one 100-ft. 35mm microfilm roll and a stack of
100 microfiches at various RH levels at 20°C.

                                                                                                                                                    32
USE OF DESICCANTS INSIDE SEALED PACKAGING

Goal
The use of moisture adsorbents inside sealed bags was investigated as an alternative to
the moisture-preconditioning procedure explored above. Using desiccants along with the
film materials inside sealed moisture-proof packages does not require a humidity-
controlled space for preparing the film materials for long-term storage. As mentioned in
the introduction, the use of adsorbents to control microclimates had been investigated
particularly as regards the preservation of acetate-based motion picture films. The method
relies on the moisture-adsorption properties of specific desiccants. Once film materials
and desiccants are enclosed inside a moisture-proof package they will exchange water
vapor until equilibrium is reached. In this research, the goal is to extract surplus water
from the film. At equilibrium, the film will have a lower water content, and its gelatin
layer will be at less risk of physical damage.

Desiccants
 Four products were initially included in this research: molecular sieve packets21 silica gel
packets,22 Art-Sorb® sheets,23 and Rhapid Gel® sheets.24 Molecular sieves are available in
packets of 12.5 grams each. Silica gel crystals (types I and II) also can be purchased as
packets of 3.9 grams each. The Art-Sorb product was purchased as a large sheet and cut
into 4 x 5-inch samples. Rhapid Gel was purchased in a roll and was also cut into 4 x 5-
inch samples. Art-Sorb and Rhapid Gel sheets are, in fact, simply a variation of the silica
gel that comes in packets. The two products have silica gel crystals embedded in different
substrates. The former is a polyethylene/polypropylene non-woven fiber matrix
impregnated with Art-Sorb particles. Rhapid Gel consists of silica gel beads embedded in
a porous polyester web. All four materials were tested in various situations as part of this
research.

Desiccant Capacity
Preliminary experiments were conducted to compare the moisture adsorption capacity of
molecular sieves and silica gel crystals. For this purpose, both desiccants were exposed to
a series of humidity levels at 20°C. The quantity of water adsorbed by each desiccant was
determined gravimetrically, and the desiccant capacity was expressed in wt %. For
molecular sieves, the calculation was based on the initial and final weights. For silica gel,
the quantity of water adsorbed was determined by thermo-gravimetric measurement (i.e.,
drying the silica gel sample at 120°C for 18 hours). Figure 23 illustrates the moisture
adsorption capacity for both desiccants expressed as water adsorbed in wt % of desiccant.
Molecular sieves and silica gel behave differently when exposed to RHs ranging from
11% to 80%. Figure 23 indicates that the silica gel tends to adsorb more moisture than the
molecular sieves. The reported data are specific to the products tested. It was notable that
different types of silica gel crystals seem to have different desiccant capacity.


21
   http://www.fpcFilm.com
22
   www.universityproducts.com
23
   http://artsorb.com
24
   http://www.apsnyc.com

                                                                                          33
                                                             100

                                                             90




                 water adsorbed as a % of desiccant weight
                                                             80                  molecular sieves

                                                             70
                                                                                 Silica Gel
                                                             60

                                                             50

                                                             40

                                                             30

                                                             20

                                                             10

                                                              0
                                                                   0   20   40            60        80   100
                                                                                 % RH

Figure 23: Moisture adsorption capacity of molecular sieves and silica gel (types I and II) at 20°C. At a
given % RH each desiccant has a fixed capacity to adsorb moisture.


Figure 23 illustrates the behavior of silica gel when it is exposed to various RH
conditions. Silica gel crystals eventually will equilibrate to the ambient conditions, and
their moisture content will depend on the RH of the surrounding environment. In turn, an
large quantity of preconditioned silica gel can control the ambient RH inside a closed
space. Such an approach is commonly used in museums to provide specific RH levels for
sensitive objects inside display cases; slight RH changes are buffered by the silica gel
crystals, which stabilize the environment by exchanging tiny amounts of water vapor
with the air.
The proposed use of desiccants inside hermetic pouches in the current research has a
different goal, which is essentially to remove moisture from the film and hold it during
storage. The capacity of the desiccant to first dry the film is fundamental in this situation.
From Figure 23 it is clear that activated silica gel (i.e., silica gel with no adsorbed water)
will be able to remove more water from moist materials. Therefore, heat activation is of
key importance when using silica gel products in this method. The challenge is to identify
the most suitable moisture-adsorbent product and to determine the appropriate amount of
desiccant to use to achieve the desired moisture equilibrium between the film, the
microclimate inside the sealed bag, and the desiccant. Several practical situations were
explored during this project.

Experiment 1
Desiccant capacity was explored by implementing the hermetic-sealing technique. For
this preliminary experiment, film was moisture-preconditioned to two high humidity


                                                                                                               34
levels: 75% and 80% RH at 20°C. Strips and 100-ft. rolls of 16mm microfilm, 100-ft.
rolls of 35mm microfilm, and 4 x 5-inch sheet films were studied. After the test film was
moisture-conditioned, the samples were assembled. Sheet films were tested as stacks of
25 sheets, both without enclosures and inside individual enclosures (paper envelopes or
polyester sleeves). Tables XII and XIII give the range of the film configurations
investigated in this experiment. Materials and desiccants were inserted in heat-sealable
aluminum foil bags along with one electronic temperature and RH data logger. Two
sealed bags were used in order to ensure against the risk of pin-holes. The packages were
sealed inside a walk-in climate-controlled chamber maintained at the conditioning
temperature and RH levels.
Tables XII and XIII describe each test sample, i.e., format and quantity of film, type and
quantity of desiccant used, and housing configuration. The amount of molecular sieves
and silica gel added are reported in grams. In practice the quantity of desiccant added was
largely determined by the content of each packet (i.e., one packet of molecular sieves
contains 12.5 grams of desiccant; one packet of silica gel contains 3.9 grams of
desiccant). These desiccant units were used as purchased to facilitate handling. The
amount of Art-Sorb® and Rhapid Gel® is reported in number of 10 x 12cm sheets.
The effect of the desiccant was evaluated by determining the weight loss of the sample
and by monitoring the microclimate RH inside the pouch. All test samples were kept at
20°C for a period of four months prior to evaluation. Tables XII and XIII report the
weigh losses for each film configuration and indicate the final microclimate RH
measured by the data logger inside the hermetically sealed bags. The temperature and RH
data indicated that after just a few weeks the inner RH conditions had stabilized.
Generally the first stage in the equilibration process is characterized by a drastic drop in
RH due to the adsorption of moisture from the air. Afterwards, the materials and
desiccants begin to equilibrate, and the microclimate RH increases gradually until full
equilibrium is reached. The temperature and RH data showed that all desiccants had a
marked impact on the materials. All test samples displayed significant weight loss due to
the removal of water by the various desiccant materials.
The amounts of molecular sieves and silica gel used with the 100-ft. 35mm microfilm
rolls were excessive and led to extremely dry conditions inside the bags containing these
samples. The RH levels below 5% indicate that the desiccant capacity was far from
exhausted. These data indicate that the ratio of desiccant to weight of film should be
drastically reduced to avoid a microclimate RH lower than 20%, the limit commonly
recommended to avoid the risk of permanent deformation of film materials. Above 20%
RH, any film distortion that occurs as a result of low RH is reversible.
Acceptable equilibrium RH levels were reached in the tests on 4 x 5-inch sheet film
stacks. Of particular interest is the impact of individual enclosures such as paper
envelopes and polyester sleeves on the final equilibrium RH.
Similar behavior was observed with 100-ft. 16mm microfilm rolls. Figure 24 illustrates
the data obtained for samples 25, 26, and 27. These samples were initially conditioned to
20°C, 80% RH. The impact of the cardboard box on the effectiveness of the desiccant can
be seen by comparing the results for 12.5 grams of molecular sieves used with two film
rolls—one in a cardboard box and one with no enclosure. The data underscore the
                                                                                         35
limiting effect of hygroscopic materials such as paper and cardboard on the effectiveness
of the desiccant on the film itself. To offset this effect, greater amounts of desiccants
must be included within the sealed packages.
Table XII: Moisture control inside moisture-proof bags using various desiccants. All materials were
moisture-preconditioned to 20°C, 75% RH.

                                                   Desiccant                   Sample
                                                                               Weight       Equilibrium
Sample      Film Configuration                                 Amount
                                            Type                                 Loss         % RH
                                                               (grams)         (grams)
                 100-ft. 35mm
   1                                   Molecular sieves         12.5              1.2             <5
                 microfilm roll
                 100-ft. 35mm
   2                                   Molecular sieves          25               1.1             <5
                 microfilm roll
                 100-ft. 35mm
   3                                      Silica gel            11.7             0.75            <15
                 microfilm roll
                 100-ft. 35mm
   4                                      Silica gel            19.5             0.85            <10
                 microfilm roll
              Stack of 25 4" x 5"
   5       sheet films in individual   Molecular sieves          25               5.2             30
                paper envelopes
              Stack of 25 4" x 5"
   6       sheet films in individual      Art-Sorb®         5 (10x12 cm)          3.7             40
                paper envelopes
              Stack of 25 4" x 5"
   7       sheet films in individual     Rhapid Gel®        10 (10x12cm)          4.7             35
                paper envelopes
              Stack of 25 4" x 5"
   8       sheet films in individual   Molecular sieves         12.5              2.4            <15
               polyester sleeves
              Stack of 25 4" x 5"
   9       sheet films in individual      Silica gel            11.7              1.2             20
               polyester sleeves
              Stack of 25 4" x 5"
   10      sheet films in individual      Art-Sorb®         3 (10x12 cm)          1.7             30
               polyester sleeves
              Stack of 25 4" x 5"
   11      sheet films in individual     Rhapid Gel®        6 (10x12cm)           1.8             25
               polyester sleeves
             25 polyester jackets
   12          each containing 5         Rhapid Gel®        4 (10x12cm)           0.4             <5
            16mm microfilm strips




                                                                                                       36
Table XIII: Moisture control inside moisture-proof bags using various desiccants. All materials were
moisture-preconditioned to 20°C, 80% RH.

                                                     Desiccant                  Sample
                                                                                Weight       Equilibrium
 Sample       Film Configuration                                 Amount
                                              Type                                Loss         % RH
                                                                 (grams)        (grams)
                  100-ft. 35mm
    13                                  Molecular sieves          12.5            1.1             <5
                  microfilm roll
                  100-ft. 35mm
    14                                  Molecular sieves           25              —              <5
                  microfilm roll
                  100-ft. 35mm
    15                                      Silica gel            11.7            0.85           <15
                  microfilm roll
                  100-ft. 35mm
    16                                      Silica gel            19.5            0.9            <10
                  microfilm roll
               Stack of 25 4" x 5"
    17      sheet films in individual   Molecular sieves           25             5.2            <40
                 paper envelopes
               Stack of 25 4" x 5"
    18      sheet films in individual      Art-Sorb®         5 (10x12 cm)         4.4             45
                 paper envelopes
               Stack of 25 4" x 5"
    19      sheet films in individual     Rhapid Gel®        10 (10x12cm)         5.8             30
                 paper envelopes
               Stack of 25 4" x 5"
    20      sheet films in individual   Molecular sieves          12.5            2.4             15
                polyester sleeves
               Stack of 25 4" x 5"
    21      sheet films in individual       Silica gel            11.7            2.0             30
                polyester sleeves
               Stack of 25 4" x 5"
    22      sheet films in individual      Art-Sorb®         3 (10x12 cm)         1.8            <35
                polyester sleeves
               Stack of 25 4" x 5"
    23      sheet films in individual     Rhapid Gel®        6 (10x12cm)          2.1             25
                polyester sleeves
               25 polyester jackets
    24          each containing 5         Rhapid Gel®        4 (10x12cm)          0.44            —
             16mm microfilm strips
    25          100-ft. 16mm roll       Molecular sieves          12.5            2.3            <10
                100-ft. 16mm roll
    26                                  Molecular sieves          12.5            2.6             25
              inside cardboard box
                100-ft. 16mm roll
    27                                      Silica gel            11.7            2.1             35
              inside cardboard box
                100-ft. 16mm roll
    28                                      Silica gel            19.5            2.4             —
              inside cardboard box
                100-ft. 16mm roll
    29                                      Silica gel             7.8            1.8             —
              inside cardboard box




                                                                                                       37
                        100
                         90
                         80
                         70
     Equilibrium % RH



                         60
                         50
                         40
                         30
                         20
                         10
                          0
                              16mm 100-ft. roll w/o   16mm 100-ft. roll inside 16mm 100-ft. roll inside
                               enclosure with 12.5    cardboard box with 12.5 cardboard box with 11.7
                               grams of molecular        grams of molecula       grams of silica gel
                                     sieves                   sieves

Figure 24: Moisture control using molecular sieves and silica gel inside hermetically sealed package. All
100-ft. 16mm microfilm rolls were initially moisture-conditioned to 20°C, 80% RH. Film was sealed inside
moisture-proof package with desiccants and one electronic data logger.


Experiment 1 provided information that will be helpful in making adjustments to the
desiccant-material ratio in various situations. It also provided practical insights into the
suitability of the desiccant materials that were studied. These are summarized in Table
XIV. Although each archivist may form his or her own opinion, it is believed that silica
gel packets may be the most practical option. They have the advantages of being
available in small-sized units and having high moisture-adsorption capacity, and they can
be reactivated simply by heating in a dry oven at temperatures between 118° and 127°C
for at least twelve hours. Molecular sieves are a ready-to-use alternative.




                                                                                                          38
Table XIV: Comparison of the desiccants used in the study.
Product                 Description                  Advantages                      Disadvantages
               12.5 grams of molecular                                        Re-activation of packets as
Molecular                                   Ready to use.
               sieves in semipermeable                                        currently sold is not
 sieves                                     High desiccant capacity.
               Tyvek™ bag                                                     possible.
                                            High desiccant capacity.
               3.9 grams of silica gel
                                            Small 3.9-gram packets.           Re-activation needed prior
Silica gel     (types I and II) in Tyvek
                                            Re-activation possible by heat    to use.
               bag
                                            (118°C to 127°C).
               Art-Sorb particles
                                                                              Must be cut to size.
           ®   embedded in non-woven        Re-activation possible by heat.
Art-Sorb                                                                      Increases the volume of the
               sheet of polyethylene/       Flat.
                                                                              final package.
               polypropylene fibers
                                                                              Must be cut to size.
               Silica gel beads embedded                                      Silica gel beads tend to
 Rhapid        in porous polyester sheet.   Re-activation possible by heat.   separate from the support
  Gel®         Product contains 750 grams   Flat.                             during handling.
               of silica gel per m2                                           Greatly increases the
                                                                              volume of the final package.


Experiment 2
Based on the preliminary results of the experiment described above, a second experiment
was conducted. This one focused primarily on the use of silica gel packets and included
configurations for testing sheet films and microfiches hermetically packaged without
individual enclosures. Tables XV to XVIII report results grouped by film format: 100-ft.
35mm rolls, 100-ft. 16mm rolls, 16mm film strips, stacks of 4 x 5-inch film sheets, and
stacks of microfiches. These data show how the final equilibrium RH inside the sealed
packages varies depending on the mass of film, the presence and type of enclosures, and
the quantity and type of desiccants used. All materials were initially moisture-conditioned
to 20°C, 80% RH.
Tables XV to XVIII also report weight losses for the samples after 2.5 months of storage
at 20°C. These weight losses are converted to water adsorbed as a percentage of the
weight of the desiccant. This conversion made it possible to investigate the relationship
between desiccant capacity and the equilibrium RH inside the sealed bags after 2.5
months.
The main finding in this experiment is the fact that the results are consistent with the data
on desiccant capacity determined earlier in the project. Figure 25 shows that the data
points for water adsorbed as a percentage of the total desiccant weight (determined
empirically in experiment 2) closely follow the data points for silica gel capacity
(determined by exposure to a series of RH levels at 20°C). This information provides the
basis for predicting the amount of desiccant needed in any of a wide range of
environmental situations.
Table XV reports data obtained by testing 100-ft. 35mm microfilm rolls placed, without
enclosures, inside hermetic packages. The data indicate that similar amounts of water
were removed from film (about 1 gram) despite increasing amounts of silica gel. This
may indicate that the rate of moisture diffusion from the film was the limiting factor. The

                                                                                                       39
                                                            100

                                                             90                Silica Gel



                water adsorbed as a % of desiccant weight
                                                             80
                                                                               water adsorbed as % of silica
                                                             70
                                                                               gel inside sealed bags
                                                             60

                                                             50

                                                             40

                                                             30

                                                             20

                                                             10

                                                              0
                                                                  0              20             40             60        80         100
                                                                                                      % RH

  Figure 25: Desiccant capacity for silica gel and water adsorbed as a percent of desiccant based on
  measurements taken inside hermetic packages.

entire system had not reached equilibrium after 2.5 months. It is assumed that the
moisture adsorption process would have continued further.
One 3.9-gram packet produced an equilibrium RH of 55%, which would provide less
safety from damage, especially if it is possible that the film will be even momentarily
exposed to temperatures above 40°C.
Table XV: Moisture control inside moisture-proof bags using silica gel packets for 35mm microfilm. Film
samples were moisture preconditioned to 20°C, 80% RH. Equilibrium RH determined after 2.5 months.

                                                                             Desiccant                                  Water
        Film                                                                                         Weight Loss    Adsorbed as %   Equilibrium
    Configuration                                                                     Amount          (grams)        of Desiccant    RH (%)
                                                                      Type
                                                                                      (grams)                           Weight
    100-ft. 35mm
                                                                  Silica gel             3.9             1.2             31               55
    microfilm roll
    100-ft. 35mm
                                                                  Silica gel             7.8             1               13               25
    microfilm roll
    100-ft. 35mm
                                                                  Silica gel             11.7            1               8.5              <15
    microfilm roll

Data for 16mm microfilm are reported in Table XVI. They indicate that hermetically
packaging one 100-ft.16mm microfilm roll with three 3.9-gram silica gel packets would
produce a safe equilibrium RH. In the same experiment, it was observed that packaging a
stack of 25 16mm microfilm strips in polyester jackets with one silica gel packet

                                                                                                                                                40
produced a low RH. In this instance, the problem could be solved by increasing the mass
of film.
Table XVI: Moisture control inside moisture-proof bags using silica gel packets for 16mm microfilm. Film
samples were moisture preconditioned to 20°C, 80% RH.

                               Desiccant                             Water Adsorbed
                                                    Weight Loss                            Equilibrium
 Film Configuration                   Amount                         as % of Desiccant
                           Type                      (grams)                                RH (%)
                                      (grams)                            Weight
   16mm 100-ft. roll     Silica gel     7.8              1.7                 22                 45
   16mm 100-ft. roll
                         Silica gel     11.7             2.1                 18                 35
 inside cardboard box
  25 polyester jackets
   each containing 5
                         Silica gel      3.9            0.35                  9                <20
   16mm microfilm
         strips
  25 polyester jackets
   each containing 5
                         Silica gel      7.8            0.45                  6                <10
   16mm microfilm
         strips

Test results for various configurations of sheet film stacks are reported in Table XVII.
The results are consistent with those previously discussed, in that they show the major
impact of paper enclosures on the final equilibrium RH, regardless of the desiccant used.
For a given amount of desiccant, the presence of individual paper envelopes makes a
great difference. The addition of three silica gel packets to a bag containing only film
produced an equilibrium RH of 30%, while the same amount of desiccant produced an
equilibrium RH of 60% when individual paper enclosures were used. Comparison of the
weight losses measured for the film and the paper envelopes shows that the silica gel
adsorbed three times more water from the enclosures than from the film. This observation
will have to be factored into the guidelines. The use of individual polyester sleeves had
little, if any, impact. This behavior is consistent with polyester plastic’s recognized low
affinity for moisture. Paper, by comparison, has a great affinity for moisture. All test
samples showed the same trend.




                                                                                                      41
Table XVII: Moisture control inside moisture-proof bags using various desiccants for stacks of 25 4 x 5-
inch film sheets in various configurations. Film samples were moisture preconditioned to 20°C, 80% RH.
                                                          Weight Loss          Water
                                     Desiccant
                                                           (grams)           Adsorbed as
                                                                                              Equilibrium
 Film Configuration                                                             % of
                                           Amount                                              RH (%)
                              Type                      Film   Enclosures     Desiccant
                                           (grams)
                                                                               Weight
  Stack of 25 4" x 5"
  sheet films without       Silica gel       11.7        2           —            17               30
 individual enclosures
  Stack of 25 4" x 5"
sheet films in individual   Silica gel       11.7       0.9          2.6          30               60
    paper envelopes
  Stack of 25 4" x 5"
sheet films in individual   Silica gel       15.6       1.1          3.2          28               50
    paper envelopes
  Stack of 25 4" x 5"
sheet films in individual   Silica gel       7.8               1.6                20               35
   polyester sleeves
  Stack of 25 4" x 5"
sheet films in individual   Silica gel       15.6              2.3                15               25
   polyester sleeves
  Stack of 25 4" x 5"
                            Molecular
  sheet films without                            25     3.6          —            14               <5
                             sieves
 individual enclosures
  Stack of 25 4" x 5"
                            Molecular
sheet films in individual                        25     1.3          3.7          20               45
                             sieves
    paper envelopes
  Stack of 25 4" x 5"
                            Molecular
sheet films in individual                    12.5              2.5                20               25
                             sieves
   polyester sleeves
  Stack of 25 4" x 5"
                                               6
  sheet films without       Art-Sorb®                   2.5          —            —                20
                                         (10 x 12 cm)
 individual enclosures
  Stack of 25 4" x 5"
                                               6
sheet films in individual   Art-Sorb®                   1.3          3.8          —                50
                                         (10 x 12 cm)
    paper envelopes
  Stack of 25 4" x 5"
                                               4
sheet films in individual   Art-Sorb®                          2.2                —                30
                                         (10 x 12 cm)
   polyester sleeves

Table XVIII reports final equilibrium RH obtained by hermetically packaging stacks of
100 microfiches with molecular sieves or silica gel. All test configurations produced low
equilibrium RH levels.




                                                                                                        42
Table XVIII: Moisture control inside moisture-proof bag using molecular sieves and silica gel packets for
microfiche stacks. Samples were moisture preconditioned to 20°C, 80% RH.

                                     Desiccant                               Water
                                                                           Adsorbed as
                                                          Weight Loss                        Equilibrium
  Film Configuration                          Amount                          % of
                                 Type                      (grams)                            RH (%)
                                              (grams)                       Desiccant
                                                                             Weight
Stack of 100 microfiches
                               Molecular
   without individual                            12.5          2.1               17                5
                                sieves
       enclosures
Stack of 100 microfiches
   without individual          Silica gel        11.7          1.5               13               25
       enclosures
Stack of 100 microfiches
   without individual          Silica gel        23.4          1.8               8               <15
       enclosures

Determining the Appropriate Amount of Desiccant
The data reported in the previous sections provide mixed results regarding the
relationship between the amount of desiccant added and the resulting equilibrium RH.
The experiments demonstrated that there are a large number of variables to be evaluated
for determining the appropriate amount of moisture adsorbents to use. However, the
consistency observed between the amount of water adsorbed (expressed as a percent
desiccant) and the equilibrium RH (for silica gel and molecular sieves) was seen as the
first step toward the formulation of guidelines for a variety of situations. This goal can be
achieved by using the data developed during this research:
    1. The acceptable target was determined as 45% RH or below, at 20°C.
    2. The desiccant capacity at 20°C, 45% RH was determined (see Figure 23).
    3. The amount of water which had to be removed can be determined by using
       moisture equilibrium curve of materials (see Figures 21 and 22).
All these elements provide a way to estimate the quality of desiccant (silica gel or
molecular sieves) needed. Guidelines will be provided in a final how-to procedure.

Limitations of Using Desiccants in Hermetic Packaging
   1. The method’s main limitation is that it is difficult to determine the amount of
      desiccant to be included with the film because of the wide range of variables
      discussed above.
    2. The initial moisture content of the film should be known, which means that the
       conditions surrounding the materials, both in storage and in transit, must be
       monitored. Materials exposed to sustained high RH will need larger amounts of
       desiccant. Materials exposed to lower humidity may become excessively dry if
       packaged with too much desiccant. Knowing ambient conditions and material
       workflow is critical.


                                                                                                        43
   3. Removal of enclosures may be preferable. For certain microfilm formats,
      enclosures may make it difficult to adding desiccant packets may be difficult.
      Because plastic microfilm boxes are impermeable, the desiccant must be placed
      inside, and with a 100-ft. roll of 35mm microfilm in the box, there is little space
      left for the addition of desiccant packets. Because cardboard boxes are
      permeable, the desiccant need not be placed inside the box. However, because
      cCardboard boxes retain moisture, however, and they constitute another variable
      that must be taken into account when estimating the quantity of desiccant.
   4. The moisture capacity of the desiccants should not be allowed to diminish before
      the packages are sealed. Molecular sieves will start adsorbing moisture as soon as
      they are exposed to humidity. It is important to minimize their exposure to
      moisture to prevent loss of effectiveness.
   5. If silica gel is used, it must be activated before use. This can be accomplished by
      heating the packets for at least 12 hours in a dry oven at temperatures between
      118°C and 127°C. The use of home microwaves is also an option. Either way, the
      desiccant activation adds one more step to the procedure.
   6. Most importantly, the use of desiccants may not be a perfect solution. During this
      project, physical damage was observed in a few instances despite the addition of
      desiccants to the hermetic package. Strips of 16mm microfilms in polyester
      jackets appeared to be more prone to that problem than other formats. These
      observations may indicate that the damage occurred before the desiccant began to
      take effect. At high RH the film gelatin layer can be soft enough to flow and be
      affected by physical damage like ferrotyping.
These considerations lead to the conclusion that using desiccants in hermetic sealing
might be a viable option, particularly in moderate climates (those characterized by high,
but not extreme, RH levels), but it is not preferred to the moisture-conditioning method
discussed earlier in this report. Both approaches are compared and described in the
following section.

ALTERNATIVES FOR CONTROLLING MOISTURE INSIDE HERMETIC
PACKAGING—A COMPARISON
Two methods have been explored during this project. The first involves moisture-
conditioning the materials under controlled moderate or low RH prior to packaging. The
second relies upon the addition of desiccants to the package before it is sealed. In theory,
both approaches make sense, and it was demonstrated during the research that both are
able to significantly reduce the film water content to acceptable levels, and thus reduce
the risk of physical damage to the gelatin layer. However, these methods differ in terms
of needed equipment, material handling procedures, and amount of work involved. They
also differ in the reliability of the results they produce. Table XIX provides a short list of
requirements for each method. Table XX describes the main steps involved in each
method.




                                                                                            44
Table XIX: Requirements in terms of location, equipment, and supplies for implementing both methods.
              Moisture-Conditioning Method                           Desiccant Method
        Work space at room temperature and RH of        Work space at room temperature and
         45% or lower                                     moderate RH
        Dehumidifier                                    Shelving/rack
        Shelving/rack                                   Flat surface
        Flat surface                                    Impulse sealer
        Impulse sealer                                  Desiccants
        Aluminum foil bags                              Dry oven/microwave oven
        Gloves                                          Desiccator
                                                         Aluminum foil bags
                                                         Gloves


Moisture-Conditioning Method
This approach relies on the management of film moisture equilibration. Its
implementation requires the availability of a work space that will provide a moderate or
low humidity level at room temperature. All necessary operations should be performed
inside that room, from moisture-conditioning to hermetic sealing of the packages.
Temperature should be at a human comfort level. A lower room RH will speed the
conditioning process (see Table XXI). Depending on the location, the approach might
involve the installation of a vapor barrier and/or the use of a dehumidifier to maintain the
RH level at 45% or below. The cost of these improvements should be largely offset by
the simplicity and efficiency of the method. The smaller the room, the easier it should be
to maintain the proper environment. The room should be large enough and have enough
shelving surface to accommodate the conditioning and bagging. Material flow and
number of personnel required to do the bagging should be taken into consideration when
determining the minimum size of the conditioning/packaging room. Choosing a space
located in the middle of a larger building might also help in buffering adverse outside
climate conditions. The proper setup of the room is essential for success. Short-term
equipment or power failures may not be as dramatic as one would think. Short-term
humidity changes may have little impact on microfilm rolls; they are likely to have more
of an effect of stacks of flat films. Regular power outages could be dealt with by
anticipating them and placing the materials inside moisture-proof bags. Moisture
conditioning can be resumed when the situation is normalized.
This method involves only two steps: (1) moisture conditioning, and (2) hermetic
packaging. The management of the procedure can be as simple as letting the materials
equilibrate to the work space conditions for four weeks or less regardless of their format
or configuration. Conditioning time can be shortened by referring to the data in Table
XXI. The archivist may choose the option that is the most practical one for his or her
institution.

Desiccant Method
This approach relies on the moisture adsorption capacity of desiccants. It necessitates the
addition of an adequate amount of desiccants to reduce the water content of the film to an


                                                                                                       45
acceptable level. Determining the proper amount can be difficult, however, due to a
number of variables. The data discussed in the previous section provides some guidance.
As indicated in Table XX, silica gel requires activation prior to the first use or if it is to
be reused. The activation of silica gel is required for the film to benefit from the full
moisture adsorption capacity of the desiccant, as illustrated in Figure 23.
The fact that silica gel packets can be re-activated for multiples uses is an advantage over
molecular sieve packets. However, molecular sieves, if chosen, are ready to use.
Another potential flaw specific to this method was observed during the research. In some
instances, materials initially in equilibrium with high RH exhibited some damage (e.g.,
adhesion to plastic sleeves or jackets) despite the addition of a desiccant to the sealed
package. This suggests that the damage could have taken place before the material could
benefit from the effect of the desiccant. Storing the packages vertically to reduce the
amount of pressure on the materials inside would help to minimize that behavior.
However, the problem may not always be avoidable.
The desiccant method involves three steps: (1) determination of the amount of desiccant
to be added, (2) reactivation procedure (for silica gel only), (3) hermetic sealing. The first
step is critical. Unfortunately, it is also the most difficult step because of the number of
variables an institution may have to deal with, such as different microfilm formats,
different enclosure materials, and, above all, materials with different initial levels of
water content that must be hermetically packaged. It was not possible to test all
permutations during the research. However, this research has produced sufficient basic
information to provide useful guidelines for archivists. At this time, the conditioning
method is favored over the desiccant method because the latter appears to be less reliable
and more labor-intensive.




                                                                                                 46
 Table XX: Main steps for controlling moisture inside hermetic packaging through moisture conditioning
or the addition of desiccants.
                                Moisture Conditioning                                                        Addition of Desiccants




                                                                           DESICCANT REACTIVATION
                                                                                                     Silica gel packets can be reactivated in a dry
CONDITIONING ROOM



                         Work space should be able to accommodate                                    oven (a minimum of 12 hours at 118° to
                          shelving for conditioning materials and staff                               127°C)
                          for assembling the materials and sealing the                               Microwaves can also be used to re-activate
                          bags                                                                        silica gel
                         Work space should provide normal room                                      After re-activation silica gel packets should
                          temperature for human comfort and a                                         be kept under dry conditions (e.g., inside
                          maximum of 45% RH.                                                          sealed vessel or resealable moisture-proof
                         Lower RH is favored.                                                        bag)
                         Climate conditions should be monitored.                                    Re-activation does not apply for using
                                                                                                      molecular sieves

                         Place materials on open shelving/rack.
MOISTURE CONDITIONING




                         Exposing materials without enclosures will



                                                                           DESICCANT ADDITION
                                                                                                     Determine the mass of materials to be
                          facilitate the process.
                                                                                                      sealed inside each hermetic package.
                         Expose microfiches in stacks, expose 35mm
                                                                                                     Evaluate equilibrium RH of the materials:
                          and 16mm microfilms in rolls.
                                                                                                      80% RH or higher
                         Both film and individual enclosures must be
                                                                                                      70% to 80%
                          moisture-conditioned.
                                                                                                      60% to 70%
                         Film can be placed in individual enclosures
                                                                                                     Determine the amount of desiccant needed
                          before or after conditioning.
                                                                                                      (e.g., molecular sieves or silica gel) based
                         Duration of conditioning will depend upon
                                                                                                      on guidelines.
                          the initial RH and on conditioning-room RH.
                          Guidelines are given in Table XXI.
                         After adequate conditioning, film stacks are                               Assemble film materials, heat-sealable
                          assembled, and rolls are inserted in boxes.                                 bags, and desiccants
                         In practice, any amount of film can be sealed                              Desiccant should be exposed to the air for
HERMETIC SEALING




                                                                           HERMETIC SEALING




                          inside the same bag. Practicality and need for                              the shortest possible time to minimize any
                          future access should guide this decision.                                   loss of desiccant capacity, particularly if the
                         Larger boxes and larger aluminum foil bags                                  work space is not humidity controlled.
                          can be used.                                                               Room with high humidity should not be
                         Bags must be heat-sealed inside the                                         selected as work room if possible
                          conditioning room.                                                         Bags must be sealed immediately
                         It is recommended that two moisture-proof                                  It is recommended that two moisture-proof
                          bags be used to minimize the risk of pin-                                   bag be used to minimize the risk of pin-
                          holes.                                                                      holes
                         The sealing press must be big enough to span                               The sealing press must be big enough to
                          the full width of the bag.                                                  span the full width of the bag.
                                                                                                     Vertical storage is favored to minimize
                                                                                                      weight pressure on the flat film stacks
STORAGE




                                                                           STORAGE




                         Hermetically sealed packages can be stored                                 The use of this approach remains
                          in any environment. It is recommended,                                      questionable for materials exposed to
                          however, that hot temperatures be avoided.                                  sustained high RH for long periods of time,
                                                                                                      particularly for materials in tight plastic
                                                                                                      sleeves and microfilm jackets.




                                                                                                                                                  47
Table XXI: Guidelines for moisture-conditioning roll films and stacks of flat films in a humidity-controlled
room at normal room temperature.
                           Minimum Equilibration Time to Achieve an Equilibrium RH of 45% Based
                                         on RH in Conditioning Space at 20°C (Days)
                               20% RH           30% RH             40% RH             45% RH
                           35mm     Flat     35mm      Flat     35mm       Flat   35mm     Flat
                            Roll    Film      Roll    Film       Roll     Film      Roll   Film
                 60%          5       1        10       1.5       30        5       >30    >30
  Initial
                 70%         10      1.5       17        3       >30        8       >30    >30
Equilibrium
                 80%         15       2        24        4       >30        10      >30    >30
RH at 20°C
                 90%         20       3        30        5       >30        13      >30    >30




OBTAINING BASELINE DATA ON ENVIRONMENTAL CONDITIONS IN
SOUTHEAST ASIAN CULTURAL REPOSITORIES

Goal
The purpose of this part of the research was to monitor the environment in the collection
storage areas of 30 selected cultural repositories (national libraries and similar institutions
where master microforms might be stored) in Southeast Asia and Cuba. This data will
inform both the institutions themselves and the hermetic sealing research by providing
previously unavailable baseline data on temperature and RH conditions existent in these
locations. This overview has benefited the research by facilitating the evaluation of risk
and of probable film moisture content based on local environmental conditions.

Experimental
With the active oversight and participation of individuals at the Cornell University
Library, IPI provided two data-gathering devices known as Preservation Environment
Monitors® (PEM®s) to each of 26 selected Southeast Asian cultural repositories, with two
devices placed in the National Libraries and National Archives in Cuba. Cornell
identified the locations and arranged for the cooperation of the institutions. In addition to
the PEMs, IPI provided instructions on how to use the devices and a memory card to be
used to transfer the data back to IPI for analysis and reporting.

Participating Institutions
In the end, a total of 28 institutions agreed to participate in the project. The participants
represent ten different countries: Malaysia, Singapore, Thailand, Cambodia, the
Philippines, Myanmar, Laos, China (Hong Kong), Vietnam, and Cuba. A full list of the
participants can be found in Table XXII.
The process of sending the SRAM cards to these Southeast Asian countries was difficult,
because customs problems arose, and some items were lost in the mail. To this point, we
have data from 14 of the institutions and still have contact with some of the others. Long-
distance communication via e-mail is time-consuming, and with e-mail addresses
changing, the loss of contact was a real problem. At the end of the study IPI received 27


                                                                                                          48
temperature and RH data files from 14 institutions. All notebooks contributed to the
research are identified in Table XXII.

Monitoring Periods and Limitations for Data Analysis
In practice, it is recommended that any climate evaluation be based on temperature and
RH data collected over a period of at least one year. The reason for this is that most
storage environments are subjected to seasonal changes to greater or lesser degree
depending on the climate control system in place. The data received by IPI were collected
over various time periods. Table XXIII and Figure 26 indicate that only two data sets
were gathered over a full one-year period. Eleven data sets cover periods of two months
or less. Therefore, analysis of this data is of questionable interest, because it provides
only limited insight into the current storage environments. Nevertheless, these data added
great value to the hermetic sealing project. All results are summarized in Table XXIV.

Temperature Analysis
 The temperature and RH data collected with the PEMs provided important information
despite the short monitoring periods in some institutions. The data was analyzed at IPI
using Climate Notebook® (environmental analysis software developed by IPI). Once the
data files from the various locations were received, they were downloaded and
interpreted using Climate Notebook. This approach provided an easy way to determine
average values for temperature and RH. These results are illustrated in Figure 27. As
expected, most storage temperatures are above 20°C and some were as high as 31°C.
About 40% of the environments tested displayed a temperature of 25°C or above. Such
warm temperatures are known to promote a rate of chemical decay in most information-
recording media that is unacceptable for preservation. While chemical decay is not a
major issue for polyester-based silver gelatin materials, these high temperatures do pose a
risk for other materials that might be stored in the same areas (i.e., paper and cardboard
enclosures, paper documents, color materials, and acetate-base film). Under favorable
humidity conditions, these warm temperatures are also ideal for promoting biological
decay such as mold growth. Finally, under high RH conditions, high temperatures near
30°C are likely to produce physical damage on the gelatin layer. These average
temperature data indicate serious preservation problems in many of the institutions
included in the study.

Relative Humidity Analysis
Similar analysis was done for the RH data, and average values are illustrated in Figure
28. The results indicate that about 40% of the environments tested have an RH of 60% or
above, and about 45% of the environments displayed an average RH between 50% and
60%. Four locations indicated average RH levels of 70% and above. These high humidity
levels, when associated with warm or hot temperatures, provide favorable conditions for
mold growth, pest infestations, and physical damage to the gelatin layer of photographic
materials. In addition it is recognized that, above 50% RH, black-and-white photographic
microfilms are more likely to suffer silver oxidation, which increases the risk of
information loss.
While average RH values, by definition, provide a limited view of the humidity
conditions in a given location over time, they do make it possible to characterize that
                                                                                          49
location. However, fluctuations in RH can expose materials to levels of humidity that are
even above 70%. Whether the materials “feel” these macroenvironmental changes or not
depends largely on the RH cycling pattern and on the way the materials are housed. IPI
has studied the effect of changing environments on various materials. As a general rule,
short-term RH changes such as those induced by equipment cycling operations, usually
do not have a significant impact on film moisture content. Seasonal changes, which are
gradual and more sustained, are likely to have a greater effect. Further analysis of the
data sets collected during this study indicates that in some locations RH may vary daily
between 50% and 85%. High RH was generally observed during the day and was
associated with lower temperatures. Lower RH was observed overnight and was
associated with warmer temperatures. Such data reflect the use of climate control
primarily to provide “human-comfort” temperatures during the day.

TWPI Analysis
IPI developed the time-weighed preservation index (TWPI) to quantify the overall effect
of changing temperature and RH conditions on chemical stability. Although polyester-
based silver gelatin microfilm is composed of inherently stable materials under normal
climate conditions, TWPI analysis provides useful evaluation of the environments. Figure
29 indicates that most of the TWPI values are relatively low. Three locations have TWPI
values below 10 years. Only two environments have TWPI values greater than 50 years.
Unstable materials, such acetate base film, color materials, or magnetic tapes would be
expected to have a limited life span if stored in such environments. This is a significant
point for archivists whose collections contain a wide variety of media types. Microfilm
rolls and microfiches on polyester support are likely to be stored within larger
photographic collections along with more vulnerable media. Low TWPI values result
from warm temperatures and/or high RH. In this research, TWPI was used as another
indicator for assessing the inappropriateness of many of the environments studied for
long-term preservation.

Mold Risk Factor
The risk for biological decay was evaluated by using the mold risk factor (MRF)
calculation feature in Climate Notebook software. The goal is to quantify the risk for
mold growth based on temperature and RH. The mold risk factor is derived from an
algorithm developed by IPI with the objective of identifying climate conditions or storage
locations that present a risk for mold germination. Figure 30 illustrated the mold risk
factors calculated for all data sets. A mold risk factor of 1 represents favorable
temperature and RH conditions for germination. The greater the mold risk factor, the
greater is the potential for damage. Figure 30 identifies four data sets that definitely
present high risk for biological decay: environments with mold risk factors near 1 or
above.




                                                                                       50
Table XXII: List of participating institutions.
Countries                                Institutions                                   Notebooks
Burma          Universities Historical Research Department, Yangon
                                                                                 —
(Myanmar)      University Campus, Myanmar
                                                                                 Nat. Arch. Cambodia 1
               National Archives of Cambodia, Phnom Penh, Cambodia.
                                                                                 Nat. Arch. Cambodia 2
               Hun Sen library, Royal University of Phnom Penh, Phnom
Cambodia                                                                         Hun Sen Library 1
               Penh, Cambodia.
                                                                                 Kmer Studies Library 1
               Center for Khmer Studies Library, Siem Reap, Cambodia
                                                                                 Kmer Studies Library 2
                                                                                 U. of Philippines 1
               University of the Philippines Diliman, Quezon City, Philippines
                                                                                 U. of Philippines 2
The            University of San Carlos, Cebu City, Philippines                  —
Philippines                                                                      Nat. Lib. Philippines 1
               The National Library, Manila, Philippines
                                                                                 Nat. Lib. Philippines 2
               Rizal Library, Manila University, Manila, Philippines             —
               The National Library of Indonesia, Jakarta, Indonesia             —
               Centre for Scientific Documentation and Information, Institute
Indonesia                                                                        —
               of Sciences, Jakarta 12710, Indonesia.
               Gadjah Mada University, Main Library, Yogyakarta, Indonesia       —
               General Sciences Library, Ho Chi Minh City, Vietnam               —
                                                                                 Han-Nom Studies 1
               Han-Nom Institute, Hanoi, Vietnam
                                                                                 Han-Nom Studies 2
Vietnam                                                                          Nat. Library Vietnam 1
               The National Library of Vietnam, Hanoi, Vietnam
                                                                                 Nat. Library Vietnam 2
               The Central Library, Cantho University, Cantho City, Vietnam      —
                                                                                 Chiang Mai 1
               Chiang Mai University Library, Chiang Mai, Thailand
                                                                                 Chiang Mai 2
                                                                                 Thammasat U. Libraries1
               Thammasat University Libraries, Bangkok, Thailand
                                                                                 Thammasat U. Libraries2
Thailand
               Burapha University Library, Burapha University, Chonburi,         Burapha U. Library 1
               Thailand                                                          Burapha U. Library 2
               International Information Center, Center of Academic
                                                                                 —
               Resources, Chulalongkorn University, Bangkok, Thailand
               University of Malaya Library, Malaysia.                           —
Malaysia
               Universiti Kebangsaan Malaysia, Selangor, Malaysia                —
                                                                                 ISEAS 1
Singapore      ISEAS Library, Institute of Southeast Asian Studies, Singapore
                                                                                 ISEAS 2
                                                                                 U. of Hong Kong 1
               University of Hong Kong, Hong Kong
                                                                                 U. of Hong Kong 2
                                                                                 Lingnan 1
Hong Kong      Lingnan University Library, Hong Kong
                                                                                 Lingnan 2
                                                                                 Hong Kong Baptist 1
               Hong Kong Baptist University Library, Hong Kong
                                                                                 Hong Kong Baptist 2
               National Library of Laos, Vientiane, Lao People's Democratic
Laos                                                                             —
               Republic




                                                                                                       51
Table XXIII: Period and length of monitoring for data sets obtained for each institution.
             Notebooks                Start Date         End Date       Length of Data Set (Months)
     Nat. Arch. Cambodia 1             04/23/03          02/02/04                  10.0
     Nat. Arch. Cambodia 2             04/23/03          02/05/04                   9.0
     Hun Sen Library 1                 04/28/03          06/12/03                   2.0
     Kmer Studies Library 1            05/07/03          06/27/03                     2.0
     Khmer Studies Library 2           05/07/03          06/08/03                     1.0
     U. of Philippines 1               05/12/03          11/20/03                     6.0
     U. of Philippines 2               05/12/03          11/20/03                     6.0
     Nat. Lib. Philippines 1           05/26/03          12/01/03                     6.0
     Nat. Lib. Philippines 2           05/26/03          12/02/03                     6.0
     Han-Nom Studies 1                 06/02/03          01/06/04                     7.0
     Han Nom Studies 2                 06/02/03          01/06/04                     7.0
     Nat. Library of Vietnam 1         04/21/03          06/05/03                     2.0
     Nat. Library of Vietnam 2         04/21/03          06/06/03                     2.0
     Chiang Mai 1                      06/10/03          06/29/03                     0.5
     Chiang Mai 2                      06/10/03          06/29/03                     0.5
     Thammasat U. Libraries 1          07/18/03          07/28/04                    12.0
     Thammasat U. Libraries 2          07/18/03          07/28/04                    12.0
     Burapha U. Library 1              06/10/03          06/29/03                     0.5
     Burapha U. Library 2              05/30/03          12/01/03                     6.0
     ISEAS 1                           05/05/03          12/03/03                     8.0
     ISEAS 2                           05/05/03          12/03/03                     8.0
     U. of Hong Kong 1                 04/16/03          06/03/03                     1.5
     U. of Hong Kong 2                 04/16/03          06/02/03                     2.5
     Lingnan 1                         05/30/03          11/26/03                     2.0
     Lingnan 2                         05/30/03          11/26/03                     2.0
     Hong Kong Baptist 1               06/16/03          11/17/03                     5.0
     Hong Kong Baptist 2               06/16/03          11/17/03                     6.0




                                                                                                      52
Table XXIV: Results of climate evaluation. Due to the differences in the monitoring periods, the data sets
cannot be directly compared with each other.
        Notebooks                Avg. T (°C)       Avg. RH (%)        TWPI (Years)              MRF
Nat. Arch. Cambodia 1                31                 59                 9                    0.09
Nat. Arch. Cambodia 2                22                 40                41                    0.01
Hun Sen Library 1                    28                 28                29                    0.00
Kmer Studies Library 1               31                 65                 8                    0.21
Khmer Studies Library 2               31                 65                   8                  0.15
U. of Philippines 1                   24                 73                  16                 12.30
U. of Philippines 2                   23                 60                  23                  0.84
Nat. Lib. Philippines 1               27                 51                  19                  0.03
Nat. Lib. Philippines 2               27                 63                  14                  0.27
Han-Nom Studies 1                     24                 50                  27                  0.25
Han Nom Studies 2                     24                 74                  14                  8.57
Nat. Library of Vietnam 1             25                 65                  16                  0.31
Nat. Library of Vietnam 2             28                 66                  11                  0.25
Chiang Mai 1                          24                 58                  21                  0.00
Chiang Mai 2                          20                 58                  33                  0.01
Thammasat U. Libraries 1              23                 56                  25                  0.01
Thammasat U. Libraries 2              22                 54                  29                  0.00
Burapha U. Library 1                  20                 58                  33                  0.01
Burapha U. Library 2                  26                 71                  12                  7.51
ISEAS 1                               17                 48                  64                  0.06
ISEAS 2                               20                 41                  58                  0.28
U. of Hong Kong 1                     22                 58                  31                  0.00
U. of Hong Kong 2                     21                 70                  23                  0.94
Lingnan 1                             23                 52                  27                  0.00
Lingnan 2                             25                 53                  22                  0.12
Hong Kong Baptist 1                   24                 56                  22                  0.01
Hong Kong Baptist 2                   24                 64                  19                  0.70




                                                                                                         53
     Hong Kong Baptist 2
     Hong Kong Baptist 1
                Lingnan 2
                Lingnan 1
        U of Hong Kong 2
        U of Hong Kong 1
                 ISEAS 2
                 ISEAS 1
      Burapha U Library 2
      Burapha U Library 1
 Thammasat U Libraries 2
 Thammasat U Libraries 1
            Chiang Mai 2
            Chiang Mai 1
  Nat Library of Vietnam 2
  Nat Library of Vietnam 1
      Han Nom Studies 2
      Han-Nom Studies 1
      Nat Lib Philipines 2
     Nat Lib Philippines 1
         U of Philipines 2
        U of Philippines 1
  Khmer Studies Library 2
   Kmer Studies Library 1
        Hun Sen Library 1
    Nat Arch Cambodia 2
    Nat Arch Cambodia 1

                             0   2            4              6              8             10      12
                                                           Months


Figure 26: Length of monitoring period (in months) for data sets obtained for each institution.




                                                                                                  54
      Hong Kong Baptist 2
      Hong Kong Baptist 1
                Lingnan 2
                Lingnan 1
        U of Hong Kong 2
        U of Hong Kong 1
                  ISEAS 2
                  ISEAS 1
      Burapha U Library 2
      Burapha U Library 1
  Thammasat U Libraries 2
  Thammasat U Libraries 1
             Chiang Mai 2
             Chiang Mai 1
  Nat Library of Vietnam 2
  Nat Library of Vietnam 1
       Han Nom Studies 2
       Han-Nom Studies 1
       Nat Lib Philipines 2
      Nat Lib Philippines 1
          U of Philipines 2
         U of Philippines 1
   Khmer Studies Library 2
    Kmer Studies Library 1
        Hun Sen Library 1
     Nat Arch Cambodia 2
     Nat Arch Cambodia 1

                              0   5     10          15           20         25           30             35
                                               Average temperature in °C

Figure 27: Average temperatures determined during the study identified storage locations with warm or
hot conditions.




                                                                                                        55
      Hong Kong Baptist 2
      Hong Kong Baptist 1
                Lingnan 2
                Lingnan 1
        U of Hong Kong 2
        U of Hong Kong 1
                  ISEAS 2
                  ISEAS 1
      Burapha U Library 2
      Burapha U Library 1
  Thammasat U Libraries 2
  Thammasat U Libraries 1
             Chiang Mai 2
             Chiang Mai 1
  Nat Library of Vietnam 2
  Nat Library of Vietnam 1
       Han Nom Studies 2
       Han-Nom Studies 1
       Nat Lib Philipines 2
      Nat Lib Philippines 1
          U of Philipines 2
         U of Philippines 1
   Khmer Studies Library 2
    Kmer Studies Library 1
        Hun Sen Library 1
     Nat Arch Cambodia 2
     Nat Arch Cambodia 1

                              0   10   20   30      40       50       60      70       80       90      100
                                                           % RH

Figure 28: Average relative humidity levels identified storage locations with high potential for film
damage.




                                                                                                         56
      Hong Kong Baptist 2
      Hong Kong Baptist 1
                Lingnan 2
                Lingnan 1
        U of Hong Kong 2
        U of Hong Kong 1
                  ISEAS 2
                  ISEAS 1
      Burapha U Library 2
      Burapha U Library 1
  Thammasat U Libraries 2
  Thammasat U Libraries 1
             Chiang Mai 2
             Chiang Mai 1
  Nat Library of Vietnam 2
  Nat Library of Vietnam 1
       Han Nom Studies 2
       Han-Nom Studies 1
       Nat Lib Philipines 2
      Nat Lib Philippines 1
          U of Philipines 2
         U of Philippines 1
   Khmer Studies Library 2
    Kmer Studies Library 1
        Hun Sen Library 1
     Nat Arch Cambodia 2
     Nat Arch Cambodia 1

                              0   10    20             30              40              50   60      70
                                         Time Weighted Preservation Index (TWPI) in years



Figure 29: Time-weighted preservation index evaluation. TWPI values reflect the overall impact of
temperature and RH on chemical stability.




                                                                                                    57
      Hong Kong Baptist 2
      Hong Kong Baptist 1
                Lingnan 2
                Lingnan 1
        U of Hong Kong 2
        U of Hong Kong 1
                  ISEAS 2
                  ISEAS 1
      Burapha U Library 2
      Burapha U Library 1
  Thammasat U Libraries 2
  Thammasat U Libraries 1
             Chiang Mai 2
             Chiang Mai 1
  Nat Library of Vietnam 2
  Nat Library of Vietnam 1
       Han Nom Studies 2
       Han-Nom Studies 1
       Nat Lib Philipines 2
      Nat Lib Philippines 1
          U of Philipines 2
         U of Philippines 1
   Khmer Studies Library 2
    Kmer Studies Library 1
        Hun Sen Library 1
     Nat Arch Cambodia 2
     Nat Arch Cambodia 1

                         0.00   1.00   2.00   3.00   4.00   5.00   6.00     7.00   8.00      9.00   10.00   11.00   12.00   13.00   14.00   15.00
                                                                          Mold risk factor



Figure 30: Mold risk factor results helped to identify four storage locations presenting high risk for
biological decay manifestations such as mold growth (MRF near 1 or above).




                                                                                                                                               58
CONCLUSION

The investigation of hermetic sealing has provided a measure of the extent of the problem
faced by most libraries and archives located in hot and humid climates. This project has
increased our understanding of the importance of controlling the moisture content of
photographic materials in general and of microfilm in particular. The series of
experiments that were conducted resulted in the outline and evaluation of two alternatives
for reducing the moisture content of film materials to an acceptable level after they have
been exposed to high humidity conditions.
The evaluation of the current climate conditions in libraries and archives throughout the
Far East was made possible with the assistance of fifteen participating institutions that
provided valuable information regarding their storage environments. Despite the fact that
most of the temperature and RH monitoring times were short, the data sets demonstrated
the need for alternative storage options like hermetic sealing techniques. The warm
temperatures and average RH of 60% and above for 40% of the locations monitored
highlight the magnitude of the risk for physical damage and mold growth in microfilm
collections. Damage to the gelatin layer of microfilm through ferrotyping or blocking is
likely to result in information losses in many institutions. The urgency for investigating
hermetic sealing as a possible alternative for minimizing biological decay and physical
damage is supported by the environmental data gathered during the project.
The data developed during this research corroborates the assumption that high film
moisture content, warm temperatures, and physical pressure are conditions that can lead
to damage to the gelatin layer of photographic film. Higher film moisture content is likely
to lead to damage at lower temperatures. Based on earlier data and on the results obtained
during this research, it was concluded that the gelatin layer of photographic film in
equilibrium below 50% RH at 20°C would not be susceptible to physical damage during
long-term storage even when exposed to the warm temperatures common in tropical
climates. In a hermetic sealing situation it was demonstrated that controlling film
moisture content is key to minimizing ferrotyping and blocking during storage.
The research focused on exploring practical ways to reduce the moisture content of
materials that have been exposed to sustained high humidity. Two methods were
investigated: The first involves conditioning the “moist” materials to lower RH in an
acclimatization room before sealing them in moisture-proof packaging. The second relies
on the addition of moisture adsorbents inside the moisture-proof packaging. Any
moisture trapped inside the package remains there. High ambient humidity conditions
cannot adversely affect the bagged materials. The efficiency of both options depends
upon how well the film moisture content has been reestablished to a safe level.
The moisture conditioning method was elaborated based on the evaluation of moisture
equilibration rates for a variety of situations. The research has produced guidelines for
controlling the moisture-reconditioning process, and minimum times are suggested
according to type of film, initial climate conditions, and humidity level inside the
conditioning room. Controlling the procedure consists simply in conditioning the
materials for days or weeks depending on the film configuration and climate conditions.


                                                                                        59
This approach is believed to be the most practical and the most efficient for dealing with
materials that have been exposed to adverse RH conditions.
The use of desiccants was investigated in a wide variety of situations. The main challenge
in this part of the project was to provide sufficient guidance for easy general use of the
desiccant method. The success of the method depends primarily on determining the
amount of desiccant that is needed to remove a given quantity of water from moist film.
A series of experiments demonstrated that, for the task to succeed, numerous variables
must be controlled: type of desiccant, film format, film mass, enclosure materials, and
previous storage environments. The research investigated the relationship between
temperature, RH, and moisture content, and demonstrated that these relationships vary
greatly from one type of film to another. For example, for the same mass of film, several
times more water has to be removed from 35mm microfilm than from microfiche. The
research also produced basic information on the relationship between desiccant capacity
and equilibrium RH inside sealed packages; this information will provide guidance in the
application of the desiccant method. However, based on the data developed in this
research, the use of desiccants inside hermetic packaging is not favored over the
conditioning method for practical reasons, and more importantly, because of uncertainties
about its reliability, as expressed in Table XX. During this research it was observed that
film strips inserted in polyester jackets were affected by physical damage despite the
addition of a significant amount of desiccants. It may be assumed that the damage
occurred during the earliest part of the experiment.
The research led to the conclusion that hermetic sealing is a sound alternative for dealing
with high humidity in warm climates by controlling the microenvironment of microfilm
materials. It is further concluded that the successful implementation of sealed
microclimates requires absolute control of film moisture content. To achieve that goal,
the moisture-conditioning method is preferred to the addition of desiccants to the final
package. The main reason is that the conditioning method is more easily controlled than
the desiccant method. A step-by-step approach to each method will be made available on
the IPI web site (www.imagepermanenceinstitute.org) in the future. Finally, the
knowledge gained from the rather incomplete climate evaluations that were conducted in
several libraries and archives across the area underscores the need for further temperature
and RH monitoring. It is recommended that the participating institutions continue the
effort that was initiated during this project. Detailed knowledge of their storage
environments will have multiple practical benefits for each institution. Such knowledge
will serve the overall purpose of this research.




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