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Sealed Frames For Preservation - For Preservation

VIEWS: 187 PAGES: 17

									Sealed Frames
For Preservation

A Supplement to
Picture Framing Magazine
April 2002

by Hugh Phibbs
   Frames for Preservation
   The terms "preservation" and
"framing" fit together uneasily. Works
on paper, fabric, or animal skin can
best be preserved if they are stored in
                                                         by Hugh Phibbs

                                             polyamide, or polyester. Each of these
                                             polymers has a melting point that is
                                             higher than that of polyethylene and
                                             allows for heat bonding of the inner
                                             layer, while the outer layer remains
                                                                                         in an environment that has stable,
                                                                                         non-extreme condition and it must be
                                                                                         protected from water that might come
                                                                                         from an accident with a sprinkler
                                                                                         system, it can be sealed in a package
a dark, stable, safe environment.            intact.                                     glazed with acrylic sheet. Glass is
Framing is a form of display and as             These films can be used to isolate       needed for packages that will be
long as a frame is on view, its contents     wooden elements, such as fillets or         exposed to fluctuating or extreme
are exposed to light. Even with the          frame rabbet edges, from the contents       exterior condition and when static on
ultraviolet wavelengths filtered out,        of the frame. If a sheet of one of these    the glazing might pose a problem.
light will cause change in these mate-       films is substituted for the dust cover       The last decade has seen the devel-
rials. The decision to house something       paper on the back of the frame, it can      opment of packages sealed with heat
in a frame must be made with the             isolate the contents of the frame from      and either double-sided pressure-
knowledge of the effects that long           dampness that may come from the             sensitive tape or electrical-grade hot
term exposure to light will have on          wall behind it without the creation of      melt glue. Designs have evolved to
that item.                                   a highly sealed package in the frame.       accommodate both matted works and
   The frame can provide invaluable          Finally, they can also be used to create    works that have the form of paintings
protection for its contents against          packages that seal in the proper condi-     on either stretched canvas or on
mishandling and physical accidents. If       tions to which the matting and the          panel. These developments and tech-
it is properly designed, it can shield its   framed item have been acclimated and        niques have been described as they
contents from physical and chemical          can maintain those conditions indefi-       have come into service and are gath-
pollution and from the effects of fluc-      nitely, if vapor-barrier glazing is used.   ered, here, into the first complete
tuating and extremes of relative                Glass is crystalline enough to func-     overview of this topic.
humidity. These last features have           tion as a vapor-barrier, and if it is
become more widely available in the          used in a laminate, with two lites of       Some Cautions with Relative
last decade as designs for highly sealed     glass bonded together or with glass         Humidty
packages have been developed to              outside of acrylic sheet, it will provide     Fears about unintentionally creating
enhance the role of well-designed            both safety and a barrier to the            overly damp conditions in the mat
frames as useful preservation tools.         passage of moisture. Acrylic sheet has      package make many framers shy away
   The most important element in             less vapor-barrier potential and it will    from truly sealing frames. The vision
highly sealed framing is laminated           warp if its sides are exposed to            of mold growing inside a frame or
sealing film. This material has been         differing levels of relative humidity.      foxing occurring on the matting can
used for decades in military applica-        This means that the break-resistant         easily give one pause, and framers
tions and food and medical pack-             safety it offers must be weighed            should be applauded for their caution.
aging. Many types comprise an inner,         against the possibility that sealed         The questions surrounding relative
bonding layer of polyethylene, an            packages glazed with it can loose their     humidity (RH) are not, however, as
aluminum layer that serves as a vapor        initial conditioning, eventually. If        arcane as they might appear.
barrier, a second layer of polyethylene      such a package is kept in a climate           Extremely dry conditions are a
that bonds the aluminum to the               with conditions drier than those in         grave threat to wood and wood lami-
outer, puncture-resistant layer of           the package, it will warp in toward         nates, ivory, hides, horn, bone, many
plastic, and the outer layer. The outer      the art.                                    paint films, and glue layers. As such
layer may be made of polypropylene,             When the framed work will be kept        materials become desiccated, they can
                                                                                         April Preservation Supplement 2002_ PFM 3
crack and change shape; paper                Thymol is the most common of these.        the case of clients who bring in works
becomes brittle and more fragile.            However, many fungicides tend to           with mold from homes with well-
   When can such conditions be               discolor the paper to which they have      controlled climates. Interior walls
expected? Land areas which are far           been applied when exposed to light         which connect with attic or crawl
from sources of airborne water have          for a period of time. These fungicidal     spaces and are open to outside air may
dry climates. The high plains of our         materials are also highly volatile and     present the same problem.
Rocky Mountain region experiences            cannot be expected to protect treated         Sealing the mat/glass package can
conditions of relative humidity              materials from future infestations.        defend against both very wet or dry
which may hover around 20%                      Ultimately, the simplest answer to      conditions, but the framer must be
annually. Collectors in that region          the problem of mold and mildew is to       familiar with proper sealing tech-
would do well to focus on items              avoid damp conditions. To accom-           niques, as well as with management of
made of metal and to avoid leather,          plish this, one must appreciate the        condition in the shop. This way, the
wood, and the like.                          varied sources of high relative            contents will be properly conditioned
   When a residence is heated, air           humidity.                                  before the seal is made.
from the furnace will be desiccated.            Those who live very close to the           Keeping the relative humidity in a
Even an effective humidification             ocean and other salt water bodies are      frame shop within a safe range may be
unit will be hard pressed to keep the        affected not only by the moisture, but     easier than it first sounds. If one
relative humidity in the home at             also from salt which is borne inland as    considers how often items in the shop
50% at 70°F. Air which is that               an atmospheric aerosol. Metals will be     have grown mold, or how many have
humid may condense on the inside             very difficult to maintain here. Other     shown signs of new foxing, one will
of the windows of the home or its            items should be given as much protec-      have an idea of how often the relative
exterior walls.                              tion as possible.                          humidity has been dangerously high
   An item in an unsealed frame in a            In the U.S., most residents will be     for a long enough period to cause
home will likely go through a dry            affected by damp stretches of weather      damage. Even if the shop is briefly
phase during the winter. Since most          during at least part of the year. Air      exposed to dangerously high condi-
framed materials are not overly sensi-       conditioning is a first line of defense.   tions (due to power failure in the
tive to dry conditions, this is usually      Room dehumidifiers are often               summer, or flooding), the endangered
not a problem.                               designed with a bucket to collect          materials can be moved to a safer
   A dry phase will probably not occur       condensation. This would be imprac-        place or sequestered in vapor barrier
in areas which do not have significant       tical with an air conditioner, since it    materials before they become damp.
amounts of heated air in the winter.         draws so much water from the air that         Looking at the other side of the
In Hawaii or southern Florida, for           emptying its bucket would be               humidity issue, materials which will
instance, a frame may be in relatively       constant. Most homes with central air      suffer from exposure to low relative
damp conditions year round. Here,            conditioning will have conditions          humidity—wooden panels and inlay,
the framed item is in constant peril of      drier than mold requires.                  ivory, oil paintings with hide glue
foxing or mold growth. When relative            Even homes with window units are        grounds, and thick layers of gum in
humidity exceeds 65% at 70°F, mold           usually not very moist for long            watercolor and gouache—are not
may begin to grow.                           periods, since clothing and fabric on      frequently brought in for framing.
   The germinal parts, commonly              the back sides furniture would begin       When such an item is brought in
called spores, are actually conidia.         to mold if they were. Mold requires        during a dry period, it can be kept in
They are airborne and can be found           still air to grow, so air movement will    a vapor barrier bag with a conditioned
on most surfaces which have been             discourage growth on open surfaces.        blotter or board until it is framed.
exposed to the air. As the moisture          Trapped air may be a factor in the            To understand and control relative
available to them increases, they can        growth of mold, but architectural          humidity one must first be able to
begin to send rootlike filaments into        moisture is probably a greater cause.      watch it change. The least expensive
organic materials such as paper, wood,          Exterior building walls without a       monitor for relative humidity is a
or hide. They extract nutrients and          vapor barrier layer will allow moisture    cobalt salt card. A pack of five of
produce more fruiting bodies which           through and into the room. This is         these cards can be found in most
can be seen on the surface of the            true of older construction and of          preservation supply catalogues for less
infested material. If relative humidity      masonry walls. If moisture comes           than $10. If these cards are fixed to a
is lowered, their destructive growth is      through the wall into the back of the      wall in each room of the shop and to
arrested but potential for future            frame, it may become trapped,              the inside of storage units (such as
growth remains.                              making the relative humidity in the        map drawers), the staff can begin to
   In the past, antifungal materials         frame higher than that of the room.        get a sense of how the conditions
were used to address this problem.              This may be what is happening in        fluctuate in each area over a year. An
4 PFM _ April Preservation Supplement 2002
electronic hygrometer will also be           system, attention should be paid to         can keep a material supple by holding
useful in tracking the conditions of         the amount of moisture which they           its molecular structure apart so link-
the air in the shop and will provide a       contain. If a paper-based item has          ages, which would create more
check on the cards.                          come in from an automobile on a             rigidity, cannot form. This sort of
   Tracking the changes shown by the         damp day, it can be placed in a clear       material may migrate out of the
cards is likely to reveal that the shop      polyethylene bag with a cobalt salt         substance to which it was added.
will be on the dry side of 50% far           card and watched for an hour or so.         This could be especially troublesome
more often than it is on the damp            Anything to which hinges have been          if it migrated out into a closed
side, unless it is located in a basement.    attached should also be kept out of         environment.
Each building has areas of greater and       the drawers until it is thoroughly dry.        One question to ask in designing a
lesser fluctuation in relative humidity.     The same is true for any board which        package which will house something
Exterior walls are an obvious source         comes into the shop, especially if it       valuable and especially a package
for concern.                                 has been delivered during a time            which is to be sealed, is: Do any of
   Furthermore, few buildings are            when the weather is damp.                   the materials to be used have an odor?
designed with vapor barriers in their                                                    The human nose may not be as acute
walls. Plastic sheeting can slow the         Basic Frame Sealing                         as that of other mammals, but it can
passage of water vapor, but an addi-            There are a number of factors            detect a vast array of off-gassing mole-
tional layer of metal foil is required       which must be considered in the             cules. Some things like hinging paste
for complete vapor barrier protection.       context of frame sealing. What is           may have a benign odor, but a tape
Since there is little likelihood that any    being sealed in and what is being           which smells of vinegar is probably
outside walls in the shop can be             sealed out? How long can the seal be        emitting acetic acid. If the materials
expected to have complete vapor              expected to last? How effective will        to be used inside the package have
barriers in them, critical functions         the seal be under different conditions?     been determined to be stable and
such as art and board storage should         How difficult and expensive will it be      inert, the next question involves the
not be adjacent to these walls.              to establish various levels of sealing of   nature of the seal and what it will
   Interior walls must also be exam-         the package? How much benefit can           exclude.
ined to see whether they communi-            be expected from a sealed package?             Different materials can be used to
cate with attic or crawl spaces which           The materials which are to be            seal out particulate and gaseous pollu-
have untreated air in them. Warm,            sealed in a package with a work of art      tion, humidity, and light. Nothing
damp air in the summer can move              on paper should be as well known—           can give long term insulation from
into such walls and humidify them. In        and, therefore, as simple—as possible.      changes in temperature, so the effect
the winter, cold air moving through          The fewer the variables that are            of these changes on the materials and
such walls can lower their temperature       included, the fewer chances there are       on the design of the package must be
and make them condensation sites if          for an unanticipated problem. If the        considered. No package containing
the room air has been humidified.            components have been proven over            any materials which are conditioned
   In light of these considerations, the     long periods of time to have no             to higher than accepted relative
simplest strategy is a concentration on      adverse effect on delicate art which        humidity conditions can be safely
local control of humidity. Concen-           has been stored in proximity to them,       sealed. Indeed, since packages which
trating on the areas where the matting       they should work well in the future.        contain glazing will transmit water
materials and works to be framed are         Boards and hinging materials made of        vapor through their glazing, having
stored allows relatively small effort to     pure cellulose will be chemically           the materials to be sealed slightly on
produce significant results. The             similar to the paper on which the art       the dry side will permit a greater
storage drawers can be shielded with         has been done, as will vegetable starch     margin for safety. The accepted
vapor barrier film (an                       hinging paste which, like paper, is a       conditions referred to here are
aluminum/plastic laminate) which             polysaccharide. Synthetic glues have a      50% RH at 70°F or roughly 20°C.
encloses the bottom, back, top, and          less proven track record than animal           Most art on paper will do well in
sides. They will be open to the air in       and vegetable glues and pastes, but         somewhat dryer conditions than
the room, but this can be tracked. It        the best of the synthetics certainly        these, but extreme drying will cause
is also possible to make large pouches       seem to be stable and relatively inert.     the paper to become brittle and will
which will fit into the drawers them-           The inclusion of plasticizers and        cause paint films and emulsions to
selves. The pouches can be fashioned         tackifiers in pressure-sensitive adhe-      crack. If a package with damp compo-
by ironing the laminate to itself. If        sives raises more questions. These          nents is sealed, the relative humidity
separate side pieces are used, it will       additives are often not chemically          can rise as it cools and cross the
accommodate larger loads.                    linked to the material which they are       threshold at which fungal growth can
   When materials are added to the           modifying. A plasticizer, for instance,     occur (namely, 65 to 70%). A damp
6 PFM _ April Preservation Supplement 2002
package may also experience conden-          laminated glass. A double-sided pres-          Environments in which brief,
sation if it is suddenly illuminated         sure-sensitive tape is used to bond the     unavoidable periods of high relative
strongly and the paper products and          matte, polyethylene side of the film to     humidity occur can be protected
air within warm up more rapidly than         the front and edges of the glazing. If a    against by such packaging. This
the glazing.                                 window mat is used the film can be          package will eventually absorb
   Excess humidity must never be             further fused to the tape with heat         dangerous amounts of moisture if left
sealed in. The only true barrier to          provided by a household or tacking          in constantly high conditions and can
humidity is a metal film. Most coat-         iron set on medium high. The wrin-          not be used unless there will be an
ings and plastics sheets and boards          kling of the film will reveal the estab-    alteration of high and low relative
will permit the passage of water and         lishment of the bond. If a window           humidity. This highly sealed package
other vapors. The exact rate of this         mat is not used and the art comes           is only one among many options
transmission is too complicated a            within an inch or less of the edge, the     which can be employed to shelter
question to be factored in to the            laminate should be reversed so that its     framed art work from environmental
design of a framing package, but it          shiny, nylon side will be inside, as this   harm.
can be said that the thicker the mate-       will give a much superior cold bond            Pressure sensitive tapes are
rial, the slower and less efficient its      to the acrylic tape. In both cases, the     frequently used by framers to seal the
transmission.                                excess film should be trimmed off           edges of the glazing in a frame. If the
   While much of the gaseous pollu-          using the same technique employed           tape is applied between the edge of
tion which comes from our atmos-             for trimming the backing paper on           glazing and the rabbet, it may serve to
phere will be sealed out by a plastic        picture frames.                             keep dust from coming under the lip
barrier, a sacrificial
metal scavenger (such Figure 1
as active copper) or
molecular sieve is
needed to give such a
layer the kind of effi-
cacy which
approaches that of a
metal foil. Since the
metal foil will stop
the passage of water
vapor, it can not be
safely used in framing
unless the materials and environment            This package will have relatively        of the frame for a time. There is,
involved in constructing the frame           high resistance to the influx of water      however, not much dust which will
can be guaranteed to be conditioned          vapor. That resistance can be multi-        enter through this route if the frame
in the proper range. If this can not be      plied by the inclusion of properly          has a smooth, flat lip. The grip of
provided, the sealing out of pollution       conditioned silica gel impregnated          the tape on the frame will eventually
may be effected through the use of           paper. This material has many times         give up.
the plastic barrier and may be               the capacity of paper to absorb and           A more common practice is the
enhanced by the addition of the scav-        release moisture and it can buffer the      application of tape to the edges of the
enging material while water vapor is         contents of such a sealed package           glazing in the front of the package
allowed to enter and leave at a              against transmission of water vapor         and around to the edges of the
reduced rate.                                though the glazing for much longer          backing board in the rear. This leaves
   Briefly stated, the technique of basic    periods. A strip of cobalt salt             the adhesive coated side of the tape
frame sealing comprises surrounding          humidity indicator card can be placed       pointed in toward the interior of the
the properly conditioned matting             under the edge of the glazing, and on       package and the art it contains. As the
materials and the art which they             top of the edge of the window mat, so       tape ages its volitiles can infuse into
house with a solid sheet of                  that it will hide from all but the most     the package with potentially undesir-
aluminum/plastic laminate (such as           inquisitive eyes under the lip of the       able results. This problem can be
MarvelSeal 360 or 470, or Mitsubishi         frame [Figure 1]. This will permit          overcome by facing the inside of the
PE/AL/PE/PET). The sheet of lami-            the owner, who has been briefed as          tape with an impervious barrier.
nate is pulled around the sides of the       to what to look for, to monitor the           One simple candidate is the
mat package and secured to the side          condition inside the package                plastic/aluminum sheet. This material
and the front of a sheet of acrylic or       periodically.                               comes in long rolls which can be cut
8 PFM _ April Preservation Supplement 2002
into small segments on a power miter        for the normal range of conditions            allow gases to enter and exit through
box to produce small rolls of whatever      which a frame can be expected to              the acrylic. This type of package can
thickness is needed to face the part of     encounter.                                    work well in situations in which the
the pressure-sensitive tape which will         A weak point in that design is its         climate may fluctuate but will not
extend around the side of the mat           use of pressure-sensitive adhesive. This      maintain high or low RH conditions
[Figure 2]. This can be applied by          material can fail if the pressure inside      over time. If a package is to be placed
running the tape along the face of the      the package exceeds the pressure              in an environment which has high or
glass and leaving it extended from that     outside of it. That can be the case if        low relative humidity consistently over
edge while the laminate is applied to       the package experiences a change in           long periods of time, glass should be
the extended portion [Figure 3]. If the     altitude. The seams of the package at         substituted for the acrylic glazing.
polyethylene side is applied to the                                                          When a package is made using
adhesive on the tape, it will be easier       Figure 2                                    acrylic sheet, the edges of the produc-
to reposition if it goes astray and the                                                   tion paper can be peeled back along
inert nylon side will face in toward the                                                  the edges and folded over onto them-
art. Other materials such as rolled                                                       selves. This will expose the edge of the
polyester sheet can be used to perform                                                    sheet while it protects the rest and will
this role but their barrier potential is                                                  lift the straightedge up off the surface
not as great.                                                                             so that it does not become stuck in
  Any pressure-sensitive tape which is                                                    the hot glue. The glue should be
used to seal a frame will loose its hold                                                  extruded onto the edges with the same
as it ages. The more its adhesive is                                                      technique used for caulking. The glue
protected from oxygen and oxidizing                                                                         is pushed out in front
gases, the longer it will maintain its                                                                      of the nozzle. After the
bond strength. This is one the                                                                              glue has been extruded
purposes in sheltering the adhesive                                                                         along one edge, the
inside the laminate in the highly                                                               Figure 3    sheet should be turned
sealed package described here. The                                                                          so that it can next be
material to which the tape is applied       its corners are also a weak point.            set on the opposite edge. When both
must also be considered in assessing        Where one layer of tape crosses               of those lines of glue are cool, it can
the longevity of the tape bond. Tape        another, small gaps will occur which          be applied to the remaining two sides.
stuck to metal will be sheltered by         cannot be flattened by the application        Using this pattern reduces the possi-
that metal and tape suck to glazing         of heat. This can be demonstrated by          bility that the straight edge will
and plastic boards will also be some-       placing such a package under water            become fouled in still warm glue.
what sheltered by those materials.          and applying pressure. Small bubbles             If glass is required for a sealed
Aging gases can still permeate the          issuing from these corner sites are           package, it should be laminated or
carrier of the tape itself or penetrate     evidence of this problem.                     used in combination with acrylic
from its edges, but this will be signifi-      More durable packages can be made          sheet. If a package were made with
cantly less than the amount which can       if an electrical-grade hot melt adhesive      unlaminated glass and it simply
be expected to come through a paper         (such as 3M 3797 or 3748) is substi-          cracked, there might be an extended
board or wood.                              tuted for the pressure-sensitive tape.        interval in which the inside of the
  Tapes with poor quality rubber            The best of these adhesives are made          package slowly changed its condi-
family adhesives can be expected to         of polyethylene and or polypropylene.         tioning. This is because the sides of a
oxidize and release their hold sooner       Those made of polyvinyl acetate or            crack in a lite of glass are so close
than acrylic family adhesives. Tapes        ethylene vinyl acetate can be expected        together that water vapor can not
are not the most physically rugged          to give off acetic acid in time. The          move through rapidly. If the glass
method of creating a seal, but the use      better hot melt adhesives need a high         broke and pieces dislodged, the
of gasketing and pressure sealing           temperature, industrial quality gun for       package could loose its conditioning
requires so much support structure          application. This higher temperature          quite rapidly.
and expense that it is not yet practical    allows the glue to bond more success-            Before the glue is applied to the
for use in commercial framing.              fully to other polymers.                      edges of the glass, they should be
                                               Before the glue is applied, the edges      washed with alcohol to remove any
Advanced Frame Sealing                      of the glazing sheet must be dulled so        greasy residue which might disable the
   This basic method just explained         that they will not cut through the            bond. The bond which the hot melt
will perform well as a barrier to rela-     laminate. If a package is to be made          makes to the surface of glass is less
tive humidity and can be quite useful       using acrylic sheet as its glazing, it will   adhesive than that which it makes to
                                                                                          April Preservation Supplement 2002_ PFM 9
the surface of acrylic sheet. The             When either type of work is being          When the temperature in the package
temperature of the hot melt is high           sealed, its condition and the condition    rises, the air will be able to hold more
enough that it can bond readily with          of the materials which will be sealed      moisture, which the cellulose will
the acrylic, but this is not the case         with it must be established as being in    contribute to it. The relatively high
with glass. Lines of glue must be             an appropriate range. This can be          proportion of cellulose to air in this
applied to the edges of the lite of glass     done with nothing more expensive           type of package means that there
on both sides. This permits the lami-         than a cobalt salt indicator card which    should never be a problem if the mate-
nate, which will form the skin of the         has been enclosed in a plastic bag         rials are conditioned.
package, to be secured to both sides of                                                     When a painting is enclosed, there
                                               Figure 4
the glass and then bonded to itself just                                                 will be more air in the package. The
outside the edge of the glass, creating a                                                spacer which holds the painting away
more durable seal [Figure 4].                                                            from the surface of the glazing will
   The heat needed for the creation of                                                   create an air space, as will the hollow
these packages will be the same as was                                                   in back of the painting between the
required when double-sided tape was                                                      sides of the stretcher. The wood of the
                                                Figure 5
employed: roughly three quarters of                                                      stretcher will form a highly efficient
the maximum heat which most                                                              reservoir to buffer conditions inside of
tacking irons will provide. To find the                                                  the package, and stretched canvases are
proper setting, one should practice                                                      less sensitive to fluctuations in RH
bonding the laminate to itself and to                                                    than works of art on paper.
cooled extruded hot melt. When the                                                          A painting on a wooden panel of
silver surface of the laminate film has                                                  the antique variety, however, can be
acquired a wrinkled appearance, it has         Figure 6                                  quite sensitive as it expands across its
reached bonding temperature. If it                                                       grain. These are not frequently found
maintains a smooth surface, the bond                                                     in the work stream of frame shops,
may be suspect. The film should                                                          and if one were brought in with the
always be bonded to other materials or                                                   request that it be sealed, a conservator
to itself using the matte, polyethylene                                                  should be consulted. Pressed and lami-
side as the                                                                              nated wood panels are not so reactive,
bonding surface.                                                                         and can therefore be regarded as being
                         Figure 7
The shiny, nylon                                                                         more similar to stretched canvases.
side will be the                                                                            If more condition buffering is
side which faces                                                                         needed, paper impregnated with silica
the outside of the                                                                       gel can be obtained from conservation
package.                                                                                 suppliers. This material is a very effi-
   Since the adhesive used here is more       along with the material in question for    cient reservoir for water vapor. It
difficult to apply and bond in a              a few hours. Everything which will be      works because it has an extensive
controlled manner than was the case           inside the package must be condi-          surface area to which these polar mole-
with double-sided tape, the frame may         tioned to 50% RH at 70°F.                  cules will loosely bond. Since the silica
need to be chosen or modified accord-            If conditions with more humidity        get is many times more effective than
ingly. The lip or rabbet width of the         are permitted, there may be circum-        paper as an RH reservoir, its proper
frame should be no less than 3/8", and        stances in which changes of tempera-       conditioning is critical, and that
wider dimensions will help. The               ture will cause the relative humidity to   condition must be checked before it is
allowance between the edges of the            move into a dangerous range. When a        sealed in a package.
glass and the sides of the rabbet should      window mat package for a work of art          When the package for matted works
be roughly 1/8" at each edge and 1/4"         on paper is sealed, the only air inside    is begun, the mat package is laid on a
when considered together. If a frame          will be that which is between the          sheet of plastic/aluminum laminate
which has these dimensions cannot be          fibers of both the board and the art,      which is roughly 1" larger than the
found, it may be possible to use deco-        and that which is in the opening of        mat in every dimension. The glazing,
rative wooden fillet material to extend       the window. The mass of cellulose in       to which the hot melt glue has been
the lip or rabbet width of a frame            the mat and the art will readily condi-    applied, is cleaned and fitted onto the
which is available.                           tion that small quantity of air. As the    front of the mat package. When all
   There are two basic designs for            temperature of the package drops and       dust has been eliminated, the laminate
highly sealed packages, one for matted        the air can hold less moisture, the        can be tacked to the hot melt. This is
works on paper and one for paintings.         cellulose will absorb that moisture.       done by puffing it up and over the
10 PFM _ April Preservation Supplement 2002
glue and applying enough heat to fuse
it to the glue. At this point, the line of
glue will not have been flattened.
   The heating proceeds along each side
toward the corners. The bonding of
the laminate to the corners is the most
important part of the sealing process,
since it is here that leaks are most
likely to occur. The laminate which has
been bonded to contiguous edges will
form a group of gathers at the corner.
This should be puffed together and
pulled toward one of the sides so that
heat can be delivered to its base [Figure
5]. This material should then be pulled
over toward the other adjacent side
and heat applied to its base on that
side. Finally, the material can be puffed
over toward a line which bisects the
angle which the corner forms and heat
can be delivered to the center of the
base of this gathered portion of lami-
nate. It can then be flattened [Figure
6]. The purpose of this elaborate
heating of the corner of the package is
insuring that this folded part of the
package does not have any remaining
   When the corners have been treated,
heat should be carefully applied to the
edges so that the hot melt under the
laminate is flattened and a firm bond
is established all around the package.
One sign that the seal is good in a
particular area is the oozing of the hot
melt from under the edge of the lami-
nate toward the center of the acrylic
glazing. When the bonding is complete
and the hot melt is cool, the laminate
can be trimmed using the same tech-
nique one would use to trim the paper
on the back of a frame. The finished
edge should look like Figure 7 in cross
section. This sort of sealing should be
practiced, and the practice packages
should have a compressible material in
them so that they can be squeezed to
test whether the seal has been achieved.
A properly sealed package will not
collapse when squeezed and when
more than one has been made during
practice, production can begin.
   This package can be made water-
proof and may be useful if an item is
to be hung in a public place where it
                                             April Preservation Supplement 2002_ PFM 11
may encounter water from a sprinkler          the strips at the corners should be     along the length of this intersection.
system. Since the acrylic glazing will        drawn up so that their matte polyeth-   This will create a flap which should be
permit a minute amount of water               ylene sides face each other and are     heated on both sides to ensure that it is
vapor to pass through it, such a              aligned [Figure 11].                    fully bonded [Figure 12]. The joined
package can not be left in high                  The sides are joined to each other   edges of the material at the corners
humidity for indefinite periods. Glass        with heat beginning at the overlap of   should be bonded to the hot melt glue
can serve as an effective vapor barrier       the edge of the glass and proceeding    on the front of the glass with special
                                                                                      care to guard against the possibility of
                                                                                      remaining gaps. When the bonding of
                               Figure 8                                   Figure 9
                                                                                      the laminate to the front of the glazing
                                                                                      is complete and the corners have been
                                                                                      completed, heat should be applied to
                                                                                      the laminate where it passes over the
                                                                                      sides of the glass. The hot melt will
                                                                                      likely have extended slightly over the
                                                                                      edges of the glass, and this step will
                                                                                      bond the laminate more thoroughly
                                                                                      and will produce an edge which can be
and can be used to make packages                                                      completed more easily. When this
which will maintain their proper                                                      application of heat has been finished,
initial conditioning, but a more                                                      the front edge of the laminate may
complicated package and laminated                                                     show a ridge at its front outside edge
glass must be used.                                                                   which will be a sign of good adhesion
   This type of package uses two sepa-          Figure 10                             [Figure 13].
rate strips of plastic/aluminum lami-                                                    The glass can now be turned over
nate for each edge of the glass. One                                                  and narrower strips of the laminate can
strip will extend from the front edge                                                 be prepared. These should be cut in
                                                Figure 11
of the glass, across the depth of the                                                 lengths equal to the dimensions of the
rabbet, and on to the back of the                                                     edges of the glass. A strip of board,
frame, where it will form a bonding                                                   equal in thickness to the package,
surface [Figure 8]. The other strip will                                              should be cut so that it can be used as
be narrower and will go from the                                                      a bonding support. The narrow strips
inside edge of the glass and extend up                                                can now be heat bonded to the hot
the depth of the rabbet, but no further                                               melt on the inside of the glass and to
[Figure 9]. The wider strip is heat                                                   the inside of the wider strips [Figure
bonded onto the hot melt glue layer                                                   14]. There will now be a nylon surface
which has been applied to the front                                                   which lines the inside of the package
side of the glazing along each edge.                                                  in all but the four corner areas. The
These strips should overlap their              Figure 12a                             package will look like Figure 15 in
neighbors at the corners [Figure 10].                                                 cross-section.
   Their bonding is done in the same                                                     The remaining polyethylene surfaces
manner as was done with the acrylic                                                   can be joined to their neighbors with
sheet, with the strips first tacked in                                                heat if the package is stood on edge
place and then pressed down onto a                                                    and heat is applied to the outside of
flattened glue mass with more heat. A                                                 each corner [Figure 16]. This will
problem which may be encountered                                                      create a package which has tough walls
here is that the capacity which glass
has for retaining heat will make the                                                    Figure 14
laminate film easy to dislodge for a
longer time than is the case with
acrylic sheet. Thus, when the second                                   Figure 12b
application of heat is provided, care
must be taken that the tacking iron
                                                                        Figure 13
does not twist or otherwise dislodge
the film. The overlapping portion of
12 PFM _ April Preservation Supplement 2002
and will fit into the frame. The corner      indicative of a complete bond. More      have folds in it. These areas should be
flaps should be wrapped around the           time should be spent on the corners      given enough heat so that the folds
corners so that it can be set in the         where the material on the bottom will    are flattened .
frame and the                                                                            When the these seams are cool,
outer portion of        Figure 15                                                     their edges can be trimmed off inside
the wider strips                                                                      the outside edge of the frame, just as
folded onto the                                                                       if they were the edges of a sheet of
back of the frame                                                                     backing paper. The painting can now
[Figure 17]. If the                                                                   be secured in the package with
                                               Figure 16
bonded strips at the corners do not lie                                               padded mending plates which are
comfortably on the back of the frame,                                                 screwed into the back of the frame
they can be released from one another                                                 through the bonded portion of the
with heat which has been applied to                                                   package. The plates should be bent to
their outside surfaces so that the                                                    give them the proper shape and their
inside surfaces can be gently pulled                                                  ends, which will press on the
apart. Double-sided tape can be                                                       painting, should be given pads of
placed on the back of the frame so                                                    polyethylene foam held in place with
that it holds the laminate in place                                                   double-sided tape. When the plates
during the next steps.                                                                have been screwed in, a sheet of
   This sort of package is useful with
anything which must be enclosed                Figure 17
which does not have a window mat to
remove the edges of the work from
the heat needed to create the seal of
the package. The sealing done with
this package takes place on the back
of the frame and thus, away from its
contents. The spacer which will be
used to keep the work away from the
glazing can now be installed on the
edges of the glazing.
   In the case of paintings, the spacer
can be made of strips of radiation
cross-linked polyethylene foam which
have been cut to the proper width and
secured with acrylic double-sided tape
to the glazing after it has been given a
final cleaning. The painting can now
be installed and shimmied into place
with more strips of the polyethylene
foam. If silica gel is used, openings
should be left in the shims around the
edges of the painting so that the air in
front of the painting can be affected
by the silica gel in back.
   The package can now be closed
with a sheet of plastic/aluminum
laminate. This is cut so that it is larger
than the back of the frame and is laid
with the polyethylene side down over
the frame and its contents. It is
bonded with heat to the portion of
the strips which extend onto the back
of the frame. The heating should
produce the wrinkled appearance
                                                                                     April Preservation Supplement 2002_ PFM 13
polypropylene double-wall board can           This may be done with the use of           the glazing materials, ensuring that no
be cut so that it is slightly smaller         scavenging materials, but there is no      Newton rings will be produced by
than the back of the frame and can be         way of knowing how these materials         contact between the surface of the
secured to the frame with screws              are functioning in the enclosure. A        glazing materials. The viewer will see
through the bonded portion of the             less sealed environment, which allows      only the reflection on the surface of
laminate [Figure 18].                         for off gassing beyond the frame, is       the outer layer of glazing and their
  This sort of package can also be            probably wise.                             visual experience will not be marred
used with acrylic sheet glazing when                                                     by two sets of reflections.
paintings are being framed. If a              Placing Potential Damaging Items in           Materials such as rubber or wood
thicker type of sheet is used, it will        a Sealed Frame                             may be enclosed in a sealed package
give greater resistance to the influx of      When clients insist on housing mate-       without ventilation to the exterior of
water vapor and will allow for more           rials in a single frame which may          the frame. Sealing a rubber item in a
                                                                                         frame will at least limit its exposure to
                                                                                         atmospheric oxygen and will shield
                                                                                         metals, especially silver, from the
                                                                                         sulfur that the rubber will emit. The
                                                                                         acids and peroxides that wooden
                                                                                         items emit will affect the wood itself,
                                                                                         but should not lead to its physical
                                                                                         breakdown if the wood is sealed.
                            Figure 18                                   Figure 19           The sealed package for these sorts
                                                                                         of items should include a support
ready adhesion of the laminate to the
                                                           Figure 20
edges of the sheet. Whether glass or
acrylic sheet is used, the double thick
walls of this package give it a greater
resistance to punctures, therefore it
will endure more handling than the
package designed for matted works
and will hold a heavier load.
   The backing board must be behind           affect one another chemically, the         made of conservation-quality board
both types of packages to reduce the          accommodations the framer should           with margins large enough so that
possibility of punctures. An RH               make for these materials should be         heat can be applied to the edges (in
monitor can be included in either             tailored to suit the gases each item       order to bond the sealing laminate to
type of package. This can be done if          emits. Woods and some plastics give        the glazing) without any heat reaching
a cobalt salt card is cut so that a           off acids and peroxides, other plastics    the item itself. The inclusion of scav-
narrow strip of it can be secured             give off chlorine, rubber gives off        enging materials in the support mat
inside the package. It should be              sulfur, and oxidizing metals can           should benefit the enclosed item.
placed in an unobtrusive site under           contaminate other items that are in        These scavengers can include calcium
the lip of the frame so that it can           contact with them. Each of these           carbonate or zeolite found in
only be seen if special care is taken         materials must be isolated from other      matboard, copper-impregnated poly-
and will not be visible to the casual         items in the frame, but some of them       ethylene, silver cloth, or paper
viewer [Figure 19].                           may even need to be ventilated to the      impregnated with active charcoal.
   The need for proper conditioning           outside of the frame to slow their self-      The glass that forms the front of
of the material inside the package            destructive potential.                     the enclosure can be given a bead of
cannot be overstated. It is also unwise          Glass and coated metals are the         electrical grade, hot melt adhesive so
to seal in materials which may have           essential constituents of isolation in     that the plastic/metal laminate film
self-destructive potential. Obviously,        framing. When an isolation package is      can be bonded to its front edge with
such materials would not be included          made with glass and metal/plastic          heat. Since the package will be held
in the housing around the art, but            laminate, it can be secured in the         shut with the bonded laminate, the
when the art itself is made of such           frame behind a sheet of acrylic            item can be set in a sink formed to
materials, especially those which             glazing. The acrylic will protect the      the item’s contours and held away
produce acids which can build up              glass from breakage. The matting           from the glazing by a window mat,
over time, some provision for the             needed to cover the edges of the           without any further closure necessary.
uptake of the acid should be made.            package will separate the surfaces of      In cross-section, one such package
14 PFM _ April Preservation Supplement 2002
could look like Figure 20.                 Special Glazing Considerations
   Early plastics are a more difficult        Most frames can be successfully fit
challenge. Cellulose modified by           with either glass or acrylic sheet;
acetic, nitric, or other acids will        sealed frames have special considera-
produce those same acids over time.        tions. Acrylic has the advantage of
These materials have shown a               being virtually shatterproof in a frame
pronounced tendency to self-               and can be found in a wide variety of
destruct, and enclosure in a sealed        thickness and sizes, with or without
package may aggravate their condi-         an ultraviolet absorber. Glass has
tion as the acids accumulate and           more modest cost, low static poten-
cause further breakdown of the             tial, and can act as a vapor barrier,
cellulose. These materials are             which makes it valuable for the
difficult to maintain in the dark          creation of sealed packages. Acrylic is
and their inclusion in a frame must        hygroscopic and can transmit water
be discouraged.                            vapor. It can warp if the two sides of
   If they have to be included, they       the sheet are exposed to differing
should be isolated from anything else      levels of relative humidity.
in the frame and provisions should            For anti-reflectivity and stability in
be made so that their gaseous by-          sealed packages that are expected to
products can safely escape from the        resist climate change, glass is the only
frame. When such items are isolated        option, with its heat resistance and
in the frame, the package in which

              Figure 21

they are enclosed should be made so        vapor barrier potential. The critical
that any off gassing can only escape       problem with glass is its fragility.
out the back of the frame.                    Lamination of two lites of glass
   Here, the package should be faced       with a flexible core material is the
with glass, have sides of metal/plastic    obvious answer. The fact that most
laminate, and a back of conserva-          thin, flat glass is strengthened with
tion-quality matboard and acid-free        iron creates an aesthetic problem,
corrugated board. The backing board        since the presence of iron in the glass
should be open to the air behind the       imparts a green tint, and when this
frame. This may entail its being inset     tint is multiplied through lamination,
in the larger backing board which          the resulting color seriously affects its
supports the entire contents of the        color rendering. Glass with low iron
frame. This package could look like        content is beginning to become avail-
Figure 21.                                 able to framers, with and without
   The vast majority of materials          anti-reflective coating. Low iron, anti-
presented to framers for framing are       reflective, laminated glass has enjoyed
chemically stable and the only risk        widespread usage in museums, but its
they pose is their potential sensitivity   high cost and limited availability has
to light. When sports and other            kept it from use in general framing.
memorabilia are proposed for inclu-           The combination of no reflections,
sion in a shadow box, the possibility      utter clarity, ultraviolet control, effec-
of substitution of a facsimile and         tive vapor barrier potential, and
storage of the original material in a      shatter resistance adds up to the ulti-
box should be the first option.            mate in glazing products—virtual
                                                                                        April Preservation Supplement 2002_ PFM 15
invisibility with profound protection.        on the sheet at the appropriate point      two sets of reflections will not be
However, its cost will likely keep it in      on both. The scores must be run, or        evident enough to cause an aesthetic
the highest end of the framing                cracked open, with a combination of        distraction.
market. If the anti-reflective coatings       tapping along them with a screwdriver         This type of package will give some
are left out, the resulting product           and very gentle pressure. The tapping      protection from breakage, but a
would have all but one of those attrib-       and pressure will open the score that      strong blow to the surface of the outer
utes and should be available at a             is on the lite of glass that is on the     layer of glazing or severe corner-to-
much lower cost.                              bottom. When both scores have been         corner twisting could break the inner
   Such low iron, UV absorbing, lami-         run and this fact has been confirmed       layer of glass. This would leave the art
nated glass could be made without the         through careful examination with a         exposed to broken glass edges.
production demands (and therefore             raking light, the sheet can be gently         Reversing the layers of glass and
high cost) of AR glass. This glass            flexed along the open scores to expose     acrylic can address this problem. This
could be used in framing valuable             the plastic laminate for cutting. Once     strategy, which was suggested by
works, ensuring their safety and the          the excess has been removed, the           Virginia Ritchie, a museum preserva-
clear rendering of their colors. It           edges of the glass can be dulled with      tion framer, will entail the creation of
could be use in the creation of highly        an edge seamer.                            a thicker package, which must be
sealed packages that would not lose              When a laminated glass product is       strengthened to accommodate the
their initial conditioning over time.         not available, the simplest approach       acrylic sheet within, but it will elimi-
The only impediments to introduc-             would be to install a sheet of acrylic     nate any possibility of glass shards
tion of such a product are the need           in front of a sealed package that has      cutting the art.
for more two-millimeter, low iron             been made with glass. If the two              This package can be made using the
glass and the skill needed for sizing         glazing sheets are spaced apart with       same aluminum/plastic laminate sheet
laminated glass.                              strips of matboard, they should not        and electrical-grade hot melt adhesive
   Trimming lites of laminated glass to       touch and Newton rings should be           as the packages described earlier.
specific sizes entails scores being made      prevented. Also, the fact that there are      The hot melt that is used to seal the

16 PFM _ April Preservation Supplement 2002
package can also be used to hold the       placed so that its polyethylene side is     achieved, the package can be carefully
acrylic sheet and the glass apart.         down and its nylon side is up. It           moved to the edge of the work surface
While the bead of hot melt is being        should be adjusted so that it extends       and stationed at the proper distance
extruded onto the edges of the lite of     out from under the mat just far             so that the portion of the sheet not
glass, a similar bead can be set on the    enough that it will cover the side of       covered by the 1" strip can be folded
edges of the acrylic. This                                                             down over the edge of the table. This
latter layer of glue should be                                                         will keep it from becoming stuck to
thick enough to hold the                                                               the tacking iron when heat is used to
glazing layers far enough                                                              attach the strip to the laminate sheet
apart to avoid Newton rings.                                                           [Figure 22].
   The fact that there will be                                                           The tacking iron is now used to
an extra layer of glazing, and                                           Figure 22     bond the strips in place. When that
the spacing needed to                                                                  has been completed, the laminate is
accommodate it, means that                                                             pulled onto the hot melt glue on the
the package will be thicker                                                            front edges of the glass and bonded
than normal. In a normal                                                               with heat, as usual. The finished
package for a matted work,                                               Figure 23     package will look like the cross-
the laminate sheet should be                                                           section seen in Figure 23.
at least 1" larger than the glazing on     the package when it is pulled around          The added thickness of this type of
each side. Here the laminate should        to the front of the glazing, but it will    package will make the closure of the
be an 1 1/2" larger than the glazing       not extend around to the front of the       front corners a bit more difficult. The
on all sides.                              glazing.                                    laminate will seal best if it is pulled
   The other difference between this         When this position has been               onto the front of the glazing in a
package and an ordinary one is the
inclusion of the sheet of acrylic inside
the package. If the walls of the
package were not reinforced, the
acrylic sheet inside the package might
shift during handling and rupture the
laminate that surrounds it. The lami-
nate comprises four layers, (nylon on
the outside, polyethylene, aluminum,
and polyethylene), and if its integrity
is challenged on the inner polyeth-
ylene side, it will begin to give way
before the tougher nylon layer is
   The best way to prevent any threat
to the sides of the package from the
glazing involves reinforcing the sides
with another layer of laminate. Strips
of laminate roughly 1" wide, and as
long as the vertical and horizontal
dimensions of the glazing, should be
prepared. The cleaned glazing combi-
nation can be fitted to the front of the
mat package.
   The laminate sheet can now be laid
on the work surface with its polyeth-
ylene side up and the mat/glazing
package can be laid in the center of
the sheet. A 1" strip of appropriate
length can be slipped between the
back of the mat and the front of the
sheet of laminate. The strip should be
                                                                                      April Preservation Supplement 2002_ PFM 17
number of small folds, and the                successful corners and well-sealed      a package that is both safe and
thicker side of this package will tend        packages.                               attractive.
to reinforce the tendency of the lami-          The two layers of glazing will           Using two layers of glazing will
nate to fold only along the corner            reduce the transmission of light and    add to the cost of the frame and will
edge. A bit of practice at manipu-            low iron or water white glass is very   require the use of a frame with a
lating the laminate into multiple folds       helpful here. It can be combined        deeper rabbet. However, the labor
will lead to the production of fully          with UV-filtering acrylic to create     required for the creation of a highly
                                                                                      sealed package already increases its
                                                                                      price and the preservation benefits
                                                                                      that this technology confers on high
                                                                                      value items should be worth the extra
                                                                                         A similarly sealed package can be
                                                                                      made for enclosing paintings and
                                                                                      objects as well. However, its design
                                                                                      will differ from the matted package
                                                                                      since it cannot be sealed with heat
                                                                                      around the front margins of the
                                                                                      glazing due to the proximity to the
                                                                                      work inside the package.
                                                                                         A package that has two layers of
                                                                                      glazing will look best if the glazing
                                                                                      materials are as clear as possible.
                                                                                      Fortunately, low iron or water white
                                                                                      glass with anti-reflective coatings can
                                                                                      be had from more than one vendor
                                                                                      and will enhance the appearance of
                                                                                      the work within. However, the AR
                                                                                      glass will not cancel the reflections on
                                                                                      the acrylic and some of its efficacy
                                                                                      may be lost when it is combined with
                                                                                      the acrylic. If an ultraviolet absorber
                                                                                      is needed, it can be provided through
                                                                                      the inclusion of an absorber in the
                                                                                      acrylic or in a coating on the glass.
                                                                                         Creating the package begins with
                                                                                      the glass being thoroughly cleaned
                                                                                      and beads of electrical grade hot melt
                                                                                      adhesive being extruded onto the
                                                                                      outer edges of both sides of the glass.
                                                                                         Strips of plastic/aluminum laminate
                                                                                      can be used. Whichever material is
                                                                                      chosen, it can then be cut so that they
                                                                                      are 3" to 4" wide and longer than
                                                                                      each side of the glass by twice the
                                                                                      width of the strips.
                                                                                         The polyethylene side of these
                                                                                      strips can be bonded to the hot melt
                                                                                      with a tacking iron so that the strips
                                                                                      overlap onto the front of the glass by
                                                                                      1/8" and will overlap the neighboring
                                                                                      strips at each end. When the hot melt
                                                                                      is flattened and the surface of the
                                                                                      laminate is finely wrinkled, the bond
                                                                                      should be complete.
18 PFM _ April Preservation Supplement 2002
   The overlapping ends of the strips         The bulk of the laminate that            package should be sized so that it is
can now be folded up above the front       surrounds the edges of the glass will       1/16" smaller than the glass. That will
of the glass so that their polyethylene    probably require that the frame be          allow it to fit inside the package.
sides meet along a mitered line            rabbeted out to accommodate it. The            Its edges should be rounded with an
extending out from the corner of           glass should not be cut smaller than        edge seamer or a plastic file so that
the glass for heat bonding there.          normal to fit the frame, since that         they will not puncture the walls of the
   When the corners have been              would make the package too tight for        package. A bead of hot melt can be
bonded, the glass can be turned over       its painting.                               extruded onto the edges of one side of
and four more strips of laminate, 2"          If, instead, the rabbet dimensions of    the acrylic to form a spacer that will
wide and equal in length to the sides      frame are enlarged, the frame will          keep its surface from touching the
of the glass, can be heat bonded to        have a larger lip or rabbet width and       surface of the glass.
the inside of the outer strips. The        should cover the laminate at the edge          The cleaned acrylic can be fitted
inner strips should be positioned so       of the glass, while giving adequate         inside the cleaned glass of the
that they lap onto the bead of hot         room for the painting [Figure 24].          package, without bonding to the glass
melt on the inner surface of the glass     The acrylic that will fit inside the        or package. This will allow for the two
and they should be bonded onto the                                                     layers to be separated when a piece of
outer strips to a width, equal to the        Figure 24                                 framing detritus is spied in between
width of the tacking iron.                                                             them. A spacer of conservation-
   When this is complete for all four                                                  quality board or painted balsa can be
sides, the package can be stood on                                                     tacked onto the surface of the acrylic
edge and heat applied to the outside                                                   with hot melt to keep the painting
of the outer strips at each corner. This                                               away from its surface, before the
will form a joint that is perpendicular                                                acrylic is installed in the package.
to the plane of the glass. The package                                                    Finally, the painting is fitted into
is now ready for installation in the                                                   the package as it sits in the frame, and
frame.                                                                                 a sheet of laminate is heat bonded to

                                                                                      April Preservation Supplement 2002_ PFM 19
the outer edges of the package, where
they overlap the back side of the                  Chemical Interactions Inside the Frame
frame. The painting is secured with                   Once frame sealing is considered, a brief overview of chemical issues in framing can be useful.
pressure applied through the back                     The choices for glazing between glass and polymer sheeting does not have too many chemical consequences.
sheet of laminate by brass mending                Both types of material have long histories of intimate proximity to sensitive objects with little appreciable effect.
plates. These plates are screwed to the               When works are in contact with glass, there may be some possibility of chemical change on the part of the
back of the frame through the                     glass. The white material which can be seen as a ghost image on the glass of some old frames has proven in some
bonded part of the package and a                  cases to be sodium chloride (table salt). This may result from sodium, which is a very common component of
sheet of polypropylene double-wall is             glass, leaching out of the glass and combining with chlorine contributed by something in the environment.
screwed to the frame through that                     This is a situation which can be avoided by properly spacing the work in the frame away from the glass. Even if
same bonded outer portion of the                  salt were transferred to the surface of the paper, it may not have consequences which are too devestating. Salt has
package to protect the package and                been used in some watercolor and photographic techniques without obvious degradation of the paper.
the painting from punctures.                          When ultraviolet absorbers are included in glazing materials, they should not pose a chemical danger. In the
   This sort of enclosure, if properly            case of glasses, they will be deposited on the surface in a matrix which will contain them, or they will be in the
conditioned and sealed, will protect              laminate between two lites of glass. In the case of acrylic sheet, they will be in the body of the sheet and should
its contents for as long as the seal is           not be expected to migrate out. The presence of the ultraviolet light absorber will have the effect of reducing the
maintained. The longevity of such                 chemical reactions in the art as it removes the most energetic wavelengths and the chemical changes which they
protection is even more important in              would initiate.
a private setting than it is a museum,                The role that a frame might play in the chemical interactions within a frame package will depend on its material
where works are routinely unframed                and design. A metal frame is not likely to be made of an alloy or metal which would oxidize readily. (This is
as part of their maintenance.                     because the oxidation would be aesthetically disfiguring.) Metal coverings used on frames are also likely to be
   Our increasing experience with                 either non-tarnishing (like gold) or sealed.
such enclosures will inform our                       Thus, framers are likely to encounter anodized aluminum, karat gold, or brass, aluminum, or silver leaf which
future designs, increasing their dura-            has been coated. Each of these materials should have little chemical potential for interacting with the contents of
bility and powers of sequestration,               the frame. Indeed, metal coverings on wooden frames can reduce the potential which the wood has to affect the
but preservation must always be seen              framed material chemically.
as a continuing enterprise, where                     Since all wood has lignin binding it together, it has the potential to cause discoloring oxidation in materials to
items not left in even the most care-             which it is proximate. If the art is separated by a barrier layer lining the rabbet or by a wide enough expanse of
fully designed enclosures forever, but            mat board, (1"), it should be safe from this degradation.
are monitored regularly and carefully                 The recent advent of frames made of synthetic polymers raises the issue of their potential off gassing. The
to ensure their safe maintenance. ■               brevity of our experience with these materials means that we lack anecdotal evidence for their behavior over time.
                                                  It may be that some of them will not contribute chemically to the materials which they enclose, but until that has
                                                  been shown, it is wise to treat they as if they were as reactive as wood and provide for a barrier between them
                                                  and the art or a distinct buffering margin of mat board.
Hugh Phibbs has worked in preservation                Matting materials can provide the most chemically beneficial component of the entire frame. They can support
framing for more than 25 years; in a              the art and insulate it from physical damage without causing chemical change.
commercial shop and in                                The cellulose which is the primary constituent of mat board is chemically stable, especially in its non-branching,
the Conservation Division                         or alpha, type. A layer of pure cellulose is the best choice for a material which will come in contact with a work of
of the National Gallery
                                                  art on paper. If pigment is added throughout the board, it is unlikely to pose a chemical problem. The pigment
of Art. He was a
compiler of the                                   should be kept below the level of density at which it might rub or crock off onto the art to avoid physical problems.
Matting/Framing section                               Since the fibers which comprise the board will not receive printing, the need for harmful sizings, such as are
of the Book and Paper                             found in some papers, is not present. Any finishing or sizing of the board is likely to be benign, since manufacturers
Group of the American                             frequently use such exacting standards as the Photo Activity Test for assaying their products. When calcium
Institute for Conservation’s Treatment
                                                  carbonate or molecular sieves are added to the board, they provide more protection for the board itself and the
Outline. He is a Professional Associate of
the American Institute for Conservation and
                                                  material it houses.
a former board member of the Washington               The material which comprises the backing board is usually selected for its ability to provide rigidity and resist-
Conservation Guild. He has written “Preser-       ance to punctures without significant weight or expense. The best papers used in these boards are free of lignin and
vation Practices,” a monthly column on            harmful additives. This will extend their useful life and eliminate any possible chemical contribution to the frame
preservation and numerous preservation            package from that source. When backing boards contain plastics, they are likely to be polypropylene or poly-
supplements for Picture Framing Magazine,
                                                  styrene. These can be weakened by oxidation and ultraviolet. Since they will not be exposed to light, the latter
as well as an article on preservation for
Decor magazine. He has taught workshops           problem is not likely to result and, therefore, off gassing from that source is unlikely. Indeed, any off gassing which
for the conservation programs at Winterthur,      occurs is likely to be minimal.
NYU, and SUNY, Buffalo. He has also                   Since the backing board should be isolated from the art by at least one sheet of conservation-quality board, its
taught classes for the American Institution for   potential for reacting with the art is limited. The role it plays in sequestering the art from chemical change from
Conservation, The Smithsonian Resident
                                                  without is more relevant. Here, the polymers in the boards can slow the passage of atmospheric gasses into the
Associate’s Program, the PPFA, PFM Semi-
nars and The National Conference.
                                                  package. ■

20 PFM _ April Preservation Supplement 2002

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