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					National Preservation Office




Preservation of
Photographic Material




    NPO Preservation Guidance
    Preservation in Practice Series
Author Susie Clark
Design The British Library Design Office

The National Preservation Office is grateful to Riley
Dunn and Wilson and The Public Record Office of
Northern Ireland for sponsoring the production of
its leaflets. This does not imply endorsement by the
NPO of sponsors’ products or services.

August 1999
For more detailed information please refer to:

Museums & Galleries Commission, The Care of Photographic Materials and
Related Media. London: MGC, 1998.

Wilson, D., The Care and Storage of Photographs. London: NAPLIB, 1997.

Museums & Galleries Commission, Standards in the Museum Care of
Photographic Collections. London: MGC, 1996.
Preservation of
Photographic Material

Introduction

Photographs are housed in libraries and archives all over the world, but
photographic conservation is still a relatively new subject, particularly in the
area of chemical treatment. However, it is usually possible to prolong the life of
a photograph simply by good handling and housekeeping practices and by
providing suitable storage conditions. This leaflet provides guidelines on
handling, storage and basic housekeeping techniques.

Handling

Recommendations
s   Always have clean hands when examining photographs, and preferably wear
    lintless cotton gloves to avoid leaving finger-prints and stains on photographs.
s   Always work on a clean surface area. If necessary, cover the surface with
    cheap, plain paper, such as unprinted newspaper, which can be changed as
    soon as it becomes dirty.
s   Use two hands to hold the photograph and if possible support it with a piece
    of stiff card, especially if the photograph is fragile or brittle. Avoid touching
    the emulsion surface.
s   Remove envelopes from negatives and not vice versa. If a photograph
    appears stuck to its container, do not attempt to remove it.
s   Do not stack loose prints and glass plate negatives on top of each other :
    nothing should be placed on top of photographs.
s   Do not attempt to flatten rolled or curled prints : this job is best left to the
    conservator.
s   Support photographic albums on a book cradle to protect their structure, and
    use book snakes to hold the album open at the relevant page.

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s   Do not allow food and drink in the vicinity of all collection items. Sooner or
    later, an accident will happen. Prohibit smoking too. Even short-term
    exposure to nicotine can cause staining.
s   Avoid the use of ink, especially felt-tip pens. If photographs become at all
    damp, the ink may travel through to the image side, and the caption may
    eventually become illegible, as well as damaging the original. Use an HB
    pencil.
s   Do not use adhesive tapes, staples, pins, metal paper clips and rubber bands.
s   Supervise anyone who handles photographs, particularly new or untrained
    members of staff.
s   Examine photographs in light which has been ultra-violet filtered.
s   Wherever possible, give users a copy print rather than an original print
    to reduce damage to the original. (Care should always be taken to ensure that
    the process of copying the original does not damage it. The same care should
    be taken when scanning images for digital storage). Advise users on sensible
    handling procedures to avoid constantly returning to original material to
    produce new copies.

Housekeeping

The importance of good housekeeping is often overlooked, but it is one of the
simplest and cheapest aspects of preservation.

Recommendations
s Keep research and storage areas clean. These areas should be regularly
  vacuum cleaned, not swept. Apart from causing a build up of surface dirt on
  archival objects, dust will also cause scratches and blemishes on
  photographs.
s Check temperature and relative humidity regularly. Also check for signs of
  deterioration such as mould and insect or rodent attack. Damaged prints
  should be removed and stored separately to await conservation.
s Avoid storing archives in basements or attics. Both are prone to extreme
  environments and basements are particularly prone to flooding.
s Never place photographs near a heat source, such as hot water pipes, or
  hang them above a radiator. Do not place or store photographs in direct

                                         2
    sunlight.
s   Keep photographs out of freshly painted rooms and away from freshly painted
    objects for at least 2 weeks and preferably 4 weeks. Fresh paints may emit
    peroxides which can cause damage to photographs.
s   Keep copying machines away from the collections. Ozone, produced by
    electrostatic copy machines, is very damaging.
s   Do not allow photographs or their containers to come into contact with
    household cleaners containing ammonia or chlorine.

Storage

Many of the problems in photographic archives are a result of poor storage.
Photographs are complex objects and poor storage can cause many stresses on
the different components of a photograph.

Housing
One common cause of deterioration in photographs is the housing in which
they are enclosed. Unfortunately, many of the original enclosures for
photographs were far from ideal. However, good quality conservation storage
materials are now available in both paper/board and plastic.

Paper used for housing should:
s have a high alpha-cellulose content (above 87%).
s have a pH of 6.5-7.5.
s have an undetectable, reducible sulphur content.
s be free of lignin, pH buffers, metal particles, acid, peroxides and harmful
  sizing agents.

Silversafe® and pHoton™ paper are both made from 100% cotton fibre and are
particularly suitable for photographic storage. Museum boards are also available
which conform to the same standards.
  The most widely accepted plastic material for use as enclosures in
conservation is polyester film (eg. Melinex® or Mylar®). Any plastic used should
be free of plasticiser, (added to make it flexible), and the surface should not be
glazed or coated. Chlorinated sheeting, namely polyvinyl chloride (PVC), should

                                        3
not be used.
   A variety of enclosures is available for storage and many firms will supply
them custom-designed for special collections. Different formats and types of
material should be stored separately. Glass negatives are best stored vertically in
neutral paper enclosures and then in boxes. The boxes can be neutral pH or
acid-free (but must fulfil the other requirements above) or made from
MicroChamber®, which absorbs pollutants. Generally, only pH neutral material
should be allowed to come directly in contact with photographic material. Both
black and white film negatives and transparencies can be stored in polyester
film sleeves in photographic storage boxes or in a hanging file system in metal
cabinets. They can also be kept in purpose-made packaging in cold storage (see
page 8).
   Most prints, black and white or colour, can be stored in polyester film sleeves
with photographic museum board as a support if necessary. They should then be
placed in photographic storage boxes or files. The exceptions are prints with
delicate surfaces, such as flaking emulsion, or lifting pigments which may lift off
further in the presence of polyester film and which should also be seen by a
photographic conservator.
   Early photographic albums are often in poor condition and will benefit from
being wrapped in photographic conservation paper and put in a photographic
storage box.
   Polyvinyl chloride plastics, glassine envelopes, mechanical wood pulp papers,
Kraft papers and old photographic suppliers’ boxes (although they may be of
some interest in themselves) are all unsuitable for photographic storage.
   All filing cabinets should be made of metal with a baked enamel or powder-
coated finish. Anodised aluminium is also suitable. Polyethylene foam (eg.
Plastazote™) can be used to line shelves or drawers in order to soften hard
surfaces. While old wood may be safe, new wood must be avoided, especially if
it has been bleached or freshly painted. MicroChamber® paper/board can be
used as a temporary measure for lining existing unsuitable cabinets before
replacement.

Cellulose nitrate film - warning
Cellulose nitrate film can be extremely dangerous, especially if kept in adverse
storage conditions. Handling should be kept to a minimum and carried out only

                                         4
by knowledgeable staff or individuals. There are considerable health and safety
issues attached to any cellulose nitrate collection and the specific requirements
for their safe storage and, handling should be strictly adhered to, thereby
avoiding unnecessary risks.
   Cellulose nitrate film was produced extensively between 1889 and 1939 and
continued to be used up to approximately 1950. Some cellulose nitrate cine film
was used after this date as old stock: for information on cine film please contact
the British Film Institute.
   All nitrate film in a collection should be isolated and removed to a cool, dry,
well-ventilated area until it can be copied. Cellulose nitrate film is highly
inflammable and may spontaneously ignite in adverse conditions. The greatest
risk is with large amounts of densely packed film in poor condition. In this
                                                          o
instance, the ignition temperature may be as low as 48 C and the film should
not be placed near an external heat source.
   Once cellulose nitrate begins to burn, it produces gaseous products which
catalyse further decomposition and affect surrounding materials. Highly toxic
fumes, as well as smoke and heat, are produced very quickly. It can continue to
burn under water or carbon dioxide. It is also worth noting that if the buildings
or contents are insured, the policy may prohibit the storage of cellulose nitrate
film.
   Many institutions which do not have the facilities to store cellulose nitrate
material, copy it onto a more stable film base and then dispose of it. The local
authority or fire brigade should be contacted for advice on disposal.

Cellulose nitrate film - identification
Film identified as safety film does not have a cellulose nitrate film base. More
sophisticated tests should be carried out by a specialist photographic
conservator or an institution with the relevant facilities.

Environment

There are a number of environmental factors affecting the preservation of
photographs: temperature, relative humidity, air purity and light.




                                         5
Temperature and relative humidity
Considerable research continues to be carried out into the optimum
environment to keep photographs. Recent research has defined an area of
physically safe environmental parameters within which there are greatly varying
degrees of chemical stability. Firstly, there is the range of relative humidity
which is deemed to be physically safe, where photographs will not undergo
irreversible physical changes such as cracking emulsions and flaking. This
humidity range varies at different temperatures, as shown in the diagram below
for gelatine emulsion photographs.
                        30
                                                                                           a = 250c, 35% rh
                                             a             b                               b = 250c, 60% rh
                                                                     Gelatin
                                                                     above                 c = minus 250c, 40% rh
                        20
                                                                     Tg                    d = minus 250c, 20% rh
                                Museum                         1
                               Exhibition
                                      Std                      2          Gelatin          Diagram supplied by the
     Temperature (0c)




                        10                                                                 Museums & Galleries
                                                                          reaches TG
                                                               4          very high risk   Commission, copyright
                                                                                           Mr M McCormick-
                         0
                                                               10
                                                                                           Goodhart. (As shown in
                                                                                           the Museums and
                                                               30
                                                                                           Galleries Commission
                        -10                                                                Standards in the Museum
                                                                                           Care of Photographic
                                                                                           Collections. 1996.)
                                                               100
                        -20

                                   d              c            500
                        -30
                              0 10 20 30 40 50 60 70 80 90 100
                                            Relative Humidity (RH)




The Quadrant ABCD defines the safe range of temperature and RH for gelatin
binder photographic materials. The contour lines map the relative chemical
stability compared to a typical museum exhibition environment. When
conditions allow gelatin to go above its glass transition (Tg) rapid image
degradation can occur.

From the diagram it can be seen that varying the level of relative humidity
within the physically safe area will only increase the chemical rate of stability
by a factor of 2 or 3. However, altering the temperature within this quadrant will

                                                                      6
have a very significant effect, increasing the chemical stability from between 10
to 100-fold at lower temperatures. Those with collections already housed in a
tightly controlled relative humidity range 35-40% will see that this range falls
                                                                                 0
within the physically safe relative humidity parameters at any temperature (25 C
       0
to -25 C). However, those designing photographic storage areas may wish to
achieve an increase in chemical stability more easily by taking advantage of the
broader physically safe relative humidity range and introducing a lower
temperature.
   The beneficial effect of dropping the temperature by even a small amount can
clearly be seen. There is considerable advantage to be gained by cold storage
for more unstable material.

Cold storage
Cold storage is especially suitable for large quantities of film-based material,
particularly early safety film (cellulose acetate) used for black/white and colour
negatives and transparencies. This often has problems of stability which are very
difficult for a conservator to treat and treatment is usually not practical for the
volume of material present. The photographic material should be stored in a
humidity controlled cold vault or in an auto-defrost freezer in purpose-made
sealed packaging (and inserted in the packaging whilst in the physically safe
environmental conditions in Fig. 1). Provided that the photographs are brought
up to room temperature whilst in sealed packaging in order to avoid
condensation, the acclimatisation period for some packaging kits need only be
2-3 hours. Obviously it is cost effective to purchase packaging which can be
re-used. The process of acclimatising photographs to room temperature and
replacing them in cold storage should not cause physical damage, provided
condensation is avoided. However, frequent periods of use at room temperature
involving the removal of an object from cold storage will clearly lessen the
advantage of the increased chemical stability provided by cold storage. For
many institutions an auto-defrost freezer will be sufficient to house a distinct
collection, rather than a cold store, and also more practical.

Air pollution/purity
A number of chemicals present in the atmosphere are capable of oxidising
image silver. These include peroxides, ozone, sulphur-containing compounds

                                         7
(such as sulphur oxides and hydrogen sulphide) and nitrogen oxide. Large and
important collections, or collections stored in industrial areas may justify the use
of air-conditioning systems. However, in all collections some basic precautions
can be taken by avoiding the use of materials or equipment which emit
pollutants, such as some paints and varnishes, photocopying machines, woollen
carpets and new wood. Building work and redecoration can introduce
contaminants, and photographs should not be rehoused in these areas until
pollutants have fallen to acceptable levels.

Light and display
In storage and display areas, lights should be fitted with UV filters. Polymethyl
methacrylate (eg. Perspex™) rather than glass, provides a better protection
against UV light where prints are to be displayed. Blinds can also be used to
reduce light levels. A light level of 50 lux is the maximum recommended display
level and no photographs should be exposed to light levels of more than 100
lux for extended periods. Photographs should not be on permanent display, but
should be rotated. Particularly sensitive photographs should not be displayed at
all. The materials used for mounting display prints should conform to the same
standards as storage materials.
   Resin-coated prints are not particularly light stable, but archivally processed
silver gelatine prints are essentially stable at low light levels. However, long-
term display should be avoided where possible for salted paper, albumen and
various non-silver pigment prints. Colour materials are particularly vulnerable to
light in the presence of oxygen and moisture. The ultra-violet light spectrum is
the most damaging to photographic materials in general.
   To prolong the life of transparencies, projection should be kept to a minimum.
Some transparencies have been shown to fade noticeably after 20 minutes
exposure to a projector lamp. Colour transparencies suffer particularly from light
damage due to a relatively high level of exposure. The type of transparency used
should be chosen carefully and individual product information should be
consulted. Some will retain their original colours longer under projection,
whereas others will last longer in dark storage. Master copies should be of the
latter category ie. those that fade less in dark storage.




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National Preservation Office
The British Library
96 Euston Road
London NW1 2DB
Tel: 020 7412 7612
Fax: 020 7412 7796
E-mail: npo@bl.uk
www.bl.uk/services/preservation

National Preservation Office
supported by
The British Library
The Public Record Office
The National Library of
   Scotland
Trinity College Library Dublin
The Consortium of University
   Research Libraries
Cambridge University Library
The National Library of Wales
The Bodleian Library,
   Oxford University

				
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