Practical Aspects of Plastics Found in Archives
by ALAN CALMES
INTRODUCTION
At the end of the nineteenth century, cellulose nitrate, as a filler for pyroxlin bindings and as a
transparent substrate for photographic film, marked the advent of human-made plastics as an
information carrier. During the first half of the twentieth century, vinyl, in the form of phonograph
records, replaced wax cylinders and joined film as a plastic material for holding information. Since
1950, more and more plastics have been used in record-keeping practices. Sound recordings, for
example, have gone through a number of formats with different plastic materials, from physically
embossed grooves on Dictaphone® belts to magnetically charged particles on tape and, more
recently, to laminated laser-produced digitally encoded disk recordings. Each involves a complex
combination of plastics.
The great variety of plastics began to significantly affect archives by the mid-twentieth century. The
desire to have quick copies of paper documents led to the development of a variety of wet and dry
and sometimes heat-processed coated papers during the 1940s and 1950s. Some of these processes
involved plastics. Beginning in 1960, the plain paper electrostatic photocopier produced an image
using copolymcrs mixed with carbon black and fused to the paper surface. Early conservation
methods used plastics for the lamination of fragile documents. The document, tissue paper and
sheets of cellulose acetate were heat-pressed into a melt. This method of preservation was
developed at the Virginia State Library and the US National Archives in the 1940s. Plastic
enclosures and boxes have been used in archives, and plastic parts are found in informationrecording equipment. Additionally, paints containing plastics have been used on surfaces of shelves
and on containers, and plastic adhesives have been used to hold boxes and envelopes together.
Records are usually 20-30 years old by the time they reach the care of an archivist. Before records
are transferred to an archives, they may have been stored in harsh environmental conditions and
subjected to rough handling. Archival materials made of plastic often arrive in need of special
attention.
For example, cellulose nitrate film may arrive in an advanced state of deterioration and be highly
flammable and in need of special handling, packaging and storage; Dictaphone belts may arrive
cracked and broken. An archivist needs to know the aging characteristics of plastics, conservation
measures suitable for plastics, and copying techniques.
Some of the most important historical information of the second half of the twentieth century will
require special conservation and duplication efforts to preserve the memory of humanity. A partial
list of important events recorded on plastics would include: political debates and presidential
addresses and news conferences on radio and television; satellite mapping and environmental
observations; and motion pictures of historic events. An example of valuable information on a
plastic medium is the sound-recording of the Nuremberg trials, which were recorded on a long loop
of cellulose acetate film. The embossed grooves and bumps have near])' disappeared, as the plastic
material has gradually returned to its pre-embossed smooth stale. A special machine had to be built
with a special tracking stylus to play the loop.
DEFINITIONS
Plastics are modifications of naturally occurring, complex organic compounds or synthetic
polymers, usually consisting of long chains, produced by polymerization. A polymer consists of
linked units called monomers. Polymerization is the uniting of many monomers into a single
polymer molecule. Paper, which is a naturally produced polymer, is excluded from this discussion,
as are other polymers found in nature, such as wool, parchment or natural resins. Rubber bands,
made of natural and/or synthetic rubber, must be mentioned, however, since their deterioration has
been especially noted in archives.
The majority of plastics found in archives are thermoplastic materials, such as:
• cellulose nitrate
• cellulose acetate
• polycarbonate
• polymethyl methacrylate (PMMA or acrylic)
• nylon
• polyvinyl chloride (PVG)
• polystyrene
• polyethylene terephthalate (PETP or polyester) • polyolefms, such as polypropylene
and some thermosetting materials, such as:
• polyurethane • epoxy
• melamine
and phcnolics, such as phenol-formaldehyde and Bakelite.
EXAMPLES
Examples of plastics found in archives arc:
• cellulose nitrate film
• various cellulose acetate films
• vinyl phonograph disks
• polyester encapsulation
• polyoiefin shrink-wrapping
• polyethylene boxes and envelopes
• polyurethane binders on magentic tape
• acrylic sheets and blocks used in exhibits
• epoxy adhesives and coatings
• nylon gears.
Many product names are used by nonspecialists as generic names of plastics, such as DuPont's
Mylar for poly(ethylene terephthalate), Rohm & Haas' Plcxiglas for poly (methyl methacrylate) and
General Electric's Lexan for polycarbonate.
ADDITIVES
Plastic are seldom used in a pure state. Polyester used for encapsulation is generally described as a
simple polyester, but even it may contain some byproducts left over from the manufacturing
process, such as lubricants and some silica compounds to prevent blocking. Polypropylene and
polyethylene have antioxidants added so that they can be melted and formed into sheets or poured
into molds without undergoing oxidation. Additives increase the complex nature of plastic
materials. Lubricants in magnetic tape, for example, can ooze out of the tape onto its surface. The
reading-head of a tape-drive will collect the oozed-out lubricants and can cause the reading-head to
cither fail
to read the data or gouge into the surface of the magnetic tape, and destroy the recorded
information.
Since plastics may burn, melt and spread a fire rapidly, flame-retardants
arc sometimes added to plastic products. Sonic local fire codes require the addition of flameretardants in plastic materials found in household and office furniture and, therefore, indirectly in
plastic items that might be found in abundance inside any building. Some flame-retardants,
however, can evaporate in small quantities and affect materials in contact with them. Some halogen:,, for example, may produce, oxidants that can react with the silver halides of photographic
film.
CHANGES IN COMPOSITION
Plastics have evolved rapidly since 1950. Chemical formulas have been replaced or modified to
achieve desired results. New applications or improved materials brought about the obsolescence of
one form of plastic in favor of another. As a result, it is difficult to identify old plastics found in
archives without conducting laboratory tests.
Manufacturing processes have changed. Most plastics originally served more immediate needs and
were not designed for long life. There was almost an assumption in our society that plastic products
were disposable, and if one desired continued use of the product, it would have to be replaced by a
new and better one. This philosophy is changing, as manufactures are beginning to produce
engineering plastic, with substantial durability and environmental resistance. Paradoxically, there
are now environmental concerns that plastics are here forever; this fear has led to the development
of biodegradable plastics for throwaway products.
The need to periodically duplicate information on plastic media extends to all formats: sound
recordings, video recordings, microfilm, motion picture film, and computer tapes. How often this is
done depends on how the medium is stored and handled and on the characteristics of the plastics
used.
PHYSICAL. CHARACTERISTICS
Plastics can be rigid or flexible, soft or hard. Plastics can he molded to almost any shape. During
manufacturing processes, plastics are malleable and can be stretched as well as molded. These
attributes, convenient for making any shaped item, can cause problems later. With sufficient heat,
plastics can return to the malleable state and change shape. When stretched during a forming
process, plastics can be made into thin films; however, the polymer will con-
tinue to have a memory of an earlier state, and try to revert back to a previous condition. Many
plastic films will relax back to their umtretched dimensions if they are heated even briefly above a
transition temperature that varies from one plastic to another.
Plastics can be made with such a smooth surface that, when placed in contact with another smooth
surface, such as a photograph, pressed and then removed, the photograph will he left with a shiny
surface. This process is sometimes called ferrotyping (a term borrowed from photography,
referring to the process of transferring an image directly onto the smooth surface of a specially
prepared iron plate). Such plastic sheets should not be used in albums. Another deleterious process,
offsetting, is when plastics adhere to the ink and (oner of paper documents or to the imaging layer
of photographic prints. PVC plastic sheets have this quality because of its plasticizer (dioctyl
phthalate), which acts like a solvent in dissolving' and attracting the copolymcr ingredients of (oners
and dyes used in electrostatic copies and photographic images. Furthermore, PVC should not he used lor albums or interfiled with papers because
it is an unstable plastic that dehydrochlorinates to produce hydrogen chloride (HCl) and, with a little
water, hydrochloric acid.
Plastieizers are solutes placed in such plastics as PVC, which arc normally glass-like, to make them
soft and pliable. Such materials are not chemically bound to the polymer and, over time, may come
out of solution and be found on the, surface of the plastic from which they might evaporate if heated
or be rubbed off. Eventually, plastics that arc plasticized dry out, shrink and crack, like the
dashboard of a car. Other additives, such as oils, lubricants, antioxi-ants and cyanamides may also
ooze out onto the surface of the plastic material. The white powder found on the surfaces of old
films and tapes consists of a number of additives that have come out of solution in the plastic
support and/ or recording layer.
AGING CHARACTERISTICS
Cellulose nitrate
Originally, almost all black-and-white 35-mm motion picture film was on cellulose nitrate film. It
was used exclusively for studio work from the 1920s to the 1950s. Cellulose nitrate was not used
for color film, or for 16-mm and 8-mm home-movie film.
When ignited, cellulose nitrate burns very rapidly. Nitrate film decomposes with the emission of
nitrogen oxides. The reactions are highly exothermic an
are responsible for the self-ignition of cellulose nitrate. Despite the hazards,
commercial film makers preferred cellulose nitrate film over cellulose acetate safety film because it
was easy to handle and produced a very clear, sharp image when projected. By 1950, however, after
many theater fires, fire codes mandated the use of satefy film. During the past 10 years, after several
devastating and dangerous cellulose nitrate film vault explosions and fires, archives and libraries
have copied most cellulose nitrate film images onto safety film (a cellulose acetate or polyester
film) and disposed of the cellulose nitrate film. There remains, however, some spliced-in cellulose
nitrate film within reels of safety film. Nitrate-based film stock can be identified by feel; it is softer
and more supple than cellulose acetate or polyester film. When degrading, its appearance may be
deceiving. It is safer to have a laboratory test it.
The aging of cellulose nitrate is characterized by rapid change once the deterioration process
begins. Prior to the onset of deterioration, there i.s no serious shrinkage of the material, image
quality is good, and the images can be copied easily. 1 he kinetics of the reaction are such that there
appears to be virtually no intermediate stage between the time when the film is in good condition
and the time when it is obviously deteriorated. Archivists have seen reels of cellulose nitrate film
change from excellent to extremely poor condition in 2 months. When it deteriorates, cellulose
nitrate film produces sticky, brownish, powdery and fibrous globs.
Gases emitted from deteriorating cellulose nitrate film can initiate the process of deterioration in
neighboring films of all types. Chemically, cellulose nitrate, upon decomposition, produces its own
oxidizer and, therefore, once the chemical bonds begin to break down, a rapid autocatalytic reaction
sets in. The reaction produces its own heat, which accelerates the initial breakdown and the process
can be so fast as to produce fire and, if film is tightly compacted, an explosion. Once degradation of
a cellulose nitrate film has been spotted, the achivisl must move quickly to copy the images onto
safety film and to dispose of the cellulose nitrate film. The continued usefulness of a reel of
cellulose nitrate film depends upon good environmental conditions, such as clean, cool arid dry air.
Cellulose acetate
The same general mechanism of deterioration of cellulose nitrate occurs similarly in other cellulose
esters. The same acid hydrolysis occurs in all cellulose materials, but the other esters produce only
an acid that catalyzes further acid hydrolysis, not an oxidizer such as nitrogen dioxide in the case of
cellulose nitrate. The degradation process of cellulose acetate film takes longer than that
of cellulose nitrate film, but once started, the autocatalytic chemical reaction cannot be stopped. The
result of the self-destruction of cellulose acetate film is somewhat different from cellulose nitrate
film, in that an intermediate stage of deterioration between a good condition and a powdery
condition can be seen. Acetic acid, a product of cellulose acetate degradation, can be detected by its
vinegar odor. The presence of acidic gases and particles found in polluted air initiates the
degradation process of cellulose acetate film. Unlike nitrate him, however, the image layer is not
chemically aflected by the by-products of the decomposition of the acetate substrate.
The first safety-based films were cellulose monoacetale and cellulose diace-tate. The term safetybase was used because acetate films do not burn easily. By the 1970s, triacetate began to replace
diacctate as the favored substrate for film.
Manufacturing experience found that the diacctate substrate took diazo salts more readily than the
triacetate base and thus the diacctate base was used in diazo films until polyester began to be used
in the 1980s.
Researchers at the Image Permanence Institute in Rochester, NY, USA, arc finding little difference
between the degradation processes of cellulose diacctate film and cellulose triacetate film. One is
not necessarily more stable than the other. The process, however, might take longer with a triacetate
than with a diacctate. Within one category there are likely to be variations from one batch to
another, depending on formulas, additives and manufacturing processes.1
The long, intermediate stage of deterioration of cellulose acetate film is characterized by shrinkage.
When the cellulose acetate film base shrinks, the emulsion layer on top, which does not shrink, is
deformed into a mass of wrinkles. Since the image is within the emulsion layer, the image becomes
illegible, unless there is a way to copy or transfer the emulsion layer before the wrinkling obscures
the image. The choices arc to copy the image before this occurs or to laboriously remove and
reapply the image layer after it occurs. The greater the shrinkage, the more difficult it is to recover
the information. When motion picture film shrinks, the sprocket holes arc no longer in the right
place, making the copying process necessary to save the images difficult and expensive. The
shrinkage is uneven; consequently, engineered sprockets with a different spacing may not provide a
solution.
Until the late 1950s, cellulose acetate films were used as a very thin base material for sound
recording tape for some early video and computer tape. With age - accelerated by elevated
temperatures and high relative humidities - thin cellulose acetate tape becomes brittle and breaks
easily. Brittleness is an inevitable condition. Plasticizers used during the manufacturing process will
ooze out onto the surface of the tape in the form of white droplets that look
like powder. To complicate matters, a recording layer, such as one composed of iron oxides
dispersed in polyurethane, has characteristics of degradation different from that of the base material.
A break in cellulose acetate magnetic tape is usually clean, It can be spliced back together again
with little loss of information for an analog sound or video recording. This is different from
polyester-based magnetic tapes, which stretch considerably before breaking.
Polyester
Poly (ethylene terephthalate), commonly known as polyester or PET, entered the scene in the late
1950s. Because of its strength, even in a very thin film, it was used as the substrate for all computer
and video tapes. Soon thereafter, polyester replaced cellulose acetate as the base material for sound
recording tape. The switch from cellulose acetate to polyester-based photographic him has been
very slow. The demand for a strong, long-lasting microfilm brought about the use of polyester for
microfilm in the 1980s, but it coexisted with cellulose triacetate-based microfilm.
With the right combination oi conditions, acid hydrolysis can break the bonds between monomer
units of polyester; in the process, acids arc created that in turn break more bonds. This process, once
started, is autocatalytic. Hydrolysis can be initiated by acids present in polluted air or left over from
the manufacturing process. Oxides of nitrogen from automobile exhaust form acids in the
atmosphere that can accelerate the degradation process of plastics. Exclusion of water from the air,
that is, maintaining a low relative humidity, is an effective strategy to prevent hydrolysis. Using
scrubbing systems or treated charcoal filters to remove pollutant gasses from the air is another. The
lower the temperature, the slower the rate of chemical reactions. To slow down degradation,
carbodiimides are added to react with acids and antioxidants to react with oxygen; however, the
additives are cither used up, oozed out or evaporated out of the plastic.2,3
Polyester film is biaxially oriented or balanced. Cellulose acetate is often uniaxially stretched.
Because it is limber, polyester tape is more difficult to handle than cellulose acetate tape. Polyester
tends to respond to tensions. For example, it curls under tension. These characteristics vary wish the
thickness of the tape. The much thicker film for photographic film demonstrates different
properties, such as springiness rather than limberness. Polyester has plastic memory, and tries to go
back to its unstretched state. With emphasis on compaction, polyester-based computer magnetic
tape has become extremely thin, but there is, concomitantly, a greater degree of risk of loss of
information,
as a small amount of stretching or some other dimensional change can cause the loss of dala.
Engineering f/lastics
Engineering- plastics, such as nylon, ABS resin, polycarbonate and phenolics, have replaced metal
for machine parts in modern information-recording and
-retrieving devices. For example, video players now have more plastic machine parts than ever
before. Contrary 10 popular opinion that plastics are inexpensive substitutes for metal components,
plastic machine parts have the advantage of being lightweight, tough and wear-resistant; they do not
need lubrication and operate quietly in gear trains. Plastic machine parts are often more expensive
than the metal parts they replace. Quality is a factor with plastic parts as well as with metal parts.
The quality of the product depends upon the quality of the manufacturing process for the plastic part
and the quality of assembly into a machine.
Guidelines are needed for the long-term maintenance of plastic machine parts. They should not be
lubricated. There is a problem when part of a gear train is plastic and another part metal, because
the lubricant needed for the metal part may cause the plastic part to deteriorate. Spare parts should
be obtained before the machine becomes obsolete.
Acrylics, polycarbonates and epoxies
Acrylics, polycarbonates, epoxies, and copolymers are used as shields, supports, adhesives, coatings
and toners for information-recording systems. Very little experience exists on the use of these
plastics in archives, however. Acrylics are better known by their product names, such as Plexiglas
and Lucite, but acrylic products come in a variety of forms, from solid materials to liquids. Some
acrylic products turn yellow and become brittle upon exposure to ultraviolet light or unfiltered
sunlight. Recent materials use ultraviolet-blockers to reduce the damage caused by light. Rohm &
Haas acrylic resin Acryloid B-72 has been exhaustively tested and found to be non-yellowing and
very stable. PMMA has been used for compact disks (CD) and CD-read only memory (CD-ROM).
The digital information was pressed into the acrylic. Often, disks were also coated with epoxy.
Consumers began to note the failure of this product in the late 1980s. Beginning in 1990, CD and
CD-ROM were beginning to be mad-, from polycarbonate, which is tougher and more resistant to
change than PMMA.
Since epoxy resin is a thermosetting plastic, some types will take on a glass-
like characteristic and will break instead of bend. An cpoxy adhesive should not be used on a
flexible structure. Generally, the application of plastic adhesives is made possible by additives. As
the additives evaporate, the plastic hardens but remains bound to a surface. In some cases, however,
after all of the additives have evaporated, the adhesion fails. This is seen in pressure-sensitive
labels, once placed on archive containers, failing off after a few years. Tape splices on motionpicture film or magnetic tape eventually fail and must be replaced. Plastic adhesives can damage not
only the surface where they arc applied but also initiate the degradation of nearby areas of papers,
films and tapes.
Polyolefins and polystyrenes
Plastic containers have significant advantages over metal cans and cardboard paper boxes. They do
not corrode, and are lightweight and unaffected by high humidity or water. Polypropylene motionpicture containers are being used in some archives. There are no solvents or plasticizers in
polyolefins. However, colorants may come to the surface and cause a problem and flame-retardanls
required by lire codes may slowly, even at normal temperatures, emit small quantities of reactive
materials, which might affect the contents of the container.
Plastic cartridges can warp and cause magnetic tape io mistrack when read and to misalign when
rewound. In the latter case the edges of the tape may vub against the sides of the container. Plastic
pressure pads in magentic tape cartridges have been known to crumble after a few years. The pieces
of pad can damage the reading machine and get between the layers of tape, causing the tape to be
wound unevenly.
Because magnetic tape is thin and will sag against the flange when stored horizontally, magnetic
tape should be stored vertically, suspended on a hub; otherwise, an unevenly wound tape will result
in having its outlying edges folded under by the weight of the rest of the tape. Motion-picture film
is thicker and stiffer than magnetic tape and is stored horizontally without flanges with the film
resting on the surface of the container. The film must be wound evenly and snugly. Instead of metal,
hubs and flanges are sometimes made of polystyrene. In special cases glass has been used for
flanges. Plastic is substantially cheaper and lighter than metal or glass; thus, we can expect to sec
more plastic.
Combinations
Combinations of materials abound in archives. Some of these materials are bound together into
laminated sandwiches. For example, bound volumes con-
sist of many layers of materials glued together. Old phonograph records were constructed of a layer
of shellac, and later acrylic laminated onto glass or metal. Magnetic tape is made up of a layer of
polyurethane laminated to a substrate of polyester. Each layer responds to a different coefficient of
expansion. Changes in environmental conditions can cause the layers to separate. The chemical
products of decomposition of one layer can affect the other layer. One layer may become brittle
while the other remains flexible.
STATIC ELECTRICITY
Plastics can hold a static electric charge and can release sparks and electromagnetic radiation. Static
is a problem for the microelectronics of some machines. Some manufacturers try to mitigate the
problem of static electricity by adding an antistatic layer to the back of tape or placing an antistatic
additive directly into the plastic. Tapes coming out of long-term storage should be equilibrated at
greater than 30% relative humidity to dissipate the electrical charge and metal reels should be
grounded. Static electricity also attracts dust and grit that must be kept away from magnetic tape or
disk surfaces to prevent a reading head from bumping into them. Note that polystyrene, the plastic
material used for tape flanges, can also collect a static charge. Dust and grit arc also undesirable on
film, since they scatter light, cast shadows and scratch the emulsion. Also, it is undesirable to attract
dust and grit at the time of polyester encapsulation of documents.
OBSOLESCENCE
Rapid changes in technology during the twentieth century have compounded the problems of
maintaining information in other forms than human-readable. For example, from the 1930s through
the 1950s, sound-recorded dictation was kept on a cellulose acetate belt, sometimes referred to as a
Dictabelt from a Dictaphone. At first, the sound frequencies were embossed mechanically into the
surface of the cellulose acetate belt; later, the sound was recorded magnetically onto the surface of
the belt. A simple stylus can translate embossed sounds into an amplifier, like that used for vinyl
disk players. To play the magnetically recorded dictation on a belt, it is necessary to obtain the same
type of machine as that used to produce the recording, or research is necessary to determine the
appropriate size of stylus and use an appropriate transducer and amplifier and play the recording at
the correct speed.
The pace of technological change has quickened during the twentieth century. Vinyl records have
been in use for 50 years, analog sound recordings on
magnetic tape for 50, digital recording for 30, and formal changes are now occurring nearly every
decade. Plastics have played a role in the quickening of change by providing an infinite variety of
new materials for adaptation. For example, computer information systems are constantly being
upgraded with increased information density and reading speed, such as dye-polymers used in some
optical-magnetic recording systems to provide very-high-density storage and fast random access.
The preservation of machine-readable information depends on periodic copying. If copying is
carried out properly and in a timely manner, there is little loss of information. However, there must
be an assumption oi continuing cost to pay for periodic duplication and new hardware and software
updates.
CONCLUSION
We have ambivalent ideas about plastics. Our memory of how plastic toys break and cannot be
fixed prompts us to think of plastics as cheap, ephemeral and disposable. Certainly, most of us
would not give another person a plastic object for a keepsake. From another point oi view, seeing
plastics floating around at the beaches in seaside resorts stimulates our environmental concerns that
plastics pollute and will never go away. The replacement of metal parts with plastic parts is
accepted by some as progress and is seen as an improvement; others would argue that the switch
represents a cheapening of the product, even though it may look better.
Since plastics can be manufactured and molded into almost any shape at a fraction of the cost of
other materials, economic forces are promoting the use of plastics. With an acceptable short life
expectancy of most products today, perhaps attributable to rapid obsolescence, frequent changes in
style and the desire to reduce manufacturing costs, manufacturers are using the less expensive
plastics in products that arc virtually disposable after a few years. Some plastics, such as polyester
and melamine, however, arc expected to remain durable and to last for centuries. The various
plastics have their various environmental requirements, and as long as they are met, the plastic
materials will serve their intended uses well. Maintaining benign environmental storage conditions
is key to extending the life of any material. Constant low relative humidity between 30% and 50%
should benefit all plastics. Temperatures should be kept as low as practical, between 5°C and 20°C.
Plastics are human-made materials subject to endless changes in proprietary formulations. After a
formula has been used and the plastic product is replaced by a new model, no one knows what
formula was used or what additives were placed in the old plastic product; it is thus almost
impossible to predict the
life expectancy of the medium. Only when we know the history of the material and its chemical
composition can we reasonably expect a certain performance and life expectancy of the plastic
medium. We need the cooperation of manufacturers to reveal the complete formula of each plastic.
With advanced warning in hand, archivists, therefore, can program replacement costs to allow for a
periodic migration of information from one plastic medium to the next.
ACKNOWLEDGEMENTS
The foregoing information on plastics found in archives was derived from interviews with archivists
and technical staff in the US National Archives and Records Administration (NARA) and with
polymer chemists and photographic film and magnetic tape standards experts at the National
Institute for Standards and Technology (NIST). Susan Lee-Bechtold, Chief Chemist, and Charles
W. Mayn, sound and video recording engineer, both at NARA, and Leslie E. Smith, polymer
chemist, and Thomas Bagg, both at NIST, were particularly helpful. The views expressed in this
paper are those of the author and do not necessarily represent NARA's institutional position on the
subject.
SUMMARIES
Practicals Aspects of Plastics Found in Archives
Today a large variety of plastics exists in archives, mainly as data carriers, but also as toners in
copies, parts of machines, material for storage and preservation, etc. These materials are by no
mean uniform, but contain fillers, plasticizers, coatings, etc. To complicate the situation even more,
the formulas of these materials are continually changing. The various plastics and their ingredients
that may be found in archives are discussed together with various ways of degradation. A general
means to counter degradation is appropriate storage. Machine-readable data are stored nearly
exclusively on plastics. Preserving them requires periodic copying.
Les Plastiques dans les Archives: Aspects Pratiques
Aujourd'hui il cxiste une large variete de plastiques dans les archives, principalement comme
supports de donnees mais aussi comme pigments (toner) de copies, parties de machine, materiel
d'entreposage et de conservation, etc. Ces materiaux ne sont aucunement hornogenes mais contiennent des charges, des plastifiants, des revetcments, e(c. Pour compliquer encore plus la situation, les
formules de ces materiaux changent continuellement. On discute des diflerents plastiques presents
clans les depotes d'archives et de leurs composants ainsi que de leurs facteurs de degradation. D'une
manicre generale on pcut eviter la degradation par tin rangement approprie. Les donnees lisibles par
machine sont presqu'cxclusivement conservces sur plastiques, leur preservation necessite une copie
regulierc.
Kunststoffe in Archiven: Einige praktische Bermerkungen iu Hirer Konservierung
In Archiven gibt es heute eine Fülle von Kunststoffen, mcist als Datenträger, aber auch im Farbstoll
(Toner) von Kopien, als Gerateteile, Material zum Sohutz und zur Konservierung, u.s.vv. Dicsc
Stoffe sind nicht einheitlich; sie enthalten Weichmacher, Füllsloffe, Beschichtungen u.s.w., deren
Zusaminonsetzung sich laufend ändert. Es werden die verschiedenen in Archiven begegnenden
Kunststoflc diskutiert sowie die Vorgänge, die ihren Abbau bewirken. Generell werden diese durch
günstige Lagcrbcdingimgcn vcrlangsamt. Maschinenk'sbare Datcn, die nahezu ausschließlich auf
Kunststoir gespeichert sind, werden nur durch regelmäßiges Umkopieren dauerhaft erhaiten.
REFERENCES
1. Adelstein, P. Z.: Stability of cellulose ester base photographic film. In: Proceedings of the 133rd
S MPTE Technology Conference, October 26-29, 1991.
2. Smith, L. E. et al.: Prediction of the long-term stability of polyester-based recording media.
NBSIR 86-3474, 1986.
3. Smith, L. E.: Factors governing the long-term stability of polyester-based recording media.
Restaurator 12 (1991): 201-218.
Alan Galmes
Preservation Officer
US National Archives and Records Administration
Washington, DC 20408
USA