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Introduction
Introduction
What is cellulose acetate?
Cellulose acetate is a transparent plastic material that has
been widely used (and continues to be used today) as a base for photographic
and motion picture film, microfilm, aerial film and transparent overlays, and
for sound recordings. Originally marketed as safety film and
believed to be of archival quality, it is now known that cellulose acetate
material can undergo significant deterioration within 30-40 years if stored at
or near room temperature (Bigourdan & Reilly, 2000, p.14).
This deterioration, which initially involves the release of
acetic acid, has been termed the vinegar syndrome. The latter
stages of degradation are accompanied by shrinkage, channelling and buckling
with crystals and bubbles appearing on the surface of the film, and ultimately
embrittlement and loss of information. (For further details about the
degradation of cellulose acetate, see the Assessment Guidelines
available at http://www.nla.gov.au/anica/AssGuidelines2.doc).
This paper aims to summarise some of the important issues
emerging from the recent literature discussing preservation and storage of
cellulose acetate based film. It also provides information about cool storage
facilities in Australia. It is hoped that this information will assist
institutions considering options for the storage of their cellulose acetate
collections. For more in-depth discussion of the relevant issues the reader
should consult the cited literature.
Risks to cellulose acetate collections
Apart from the vinegar syndrome, a range of other risks to
cellulose acetate collections may exist. These include other forms of chemical
deterioration, such as colour dye fade, physical damage, fungal growth, or loss
of important information about the materials themselves arising from poor
collection control. If information about what is actually present in the
collection is not available, it is difficult to make educated storage decisions
that support preservation of the collection.
Colour film
Colour film has its own storage requirements which reflect
the instability of many of the colour dyes used in colour photographic
emulsions. This document does not attempt to deal with storage of colour
photographic materials, except to point out that cellulose acetate materials
may be colour.
Occupational Health & Safety
Occupational health and safety guidelines should be
carefully followed when working in an environment where acid vapours from
deteriorated film may be present. These acetic acid vapours, if present in
sufficient concentrations1, can pose a health risk.
| Exposure to acid vapours can cause eye irritation
including conjunctivitis, blepharitis, and keratisis, tearing (lacrimation),
irritation of the nose, throat and lungs; pharyngeal edema; skin sensitisation;
hyperkeratosis (growth of hard skin layers) and dental erosion
(Nishimura, 1995, p.378) |
Gloves made of natural rubber, neoprene or vinyl are
recommended when handling deteriorated materials, and the wearing of contact
lenses should be avoided. If substantial amounts of deteriorated material need
to be handled, it is be advisable to use a fume hood, limit exposure time
and/or ensure excellent ventilation (Nishimura, 1995, p.378).
It is often the case that cellulose nitrate negatives are
mixed in with cellulose acetate negatives. These are of significant OH & S
concern. For more information on how to identify and distinguish film base
materials, see the Assessment Guidelines available on this
website.
(1) For acetic acid the Time Weighted
Average Exposure (TWA) is 10 parts per million (ppm) or 25 milligrams per cubic
metre of air (mg m3). TWA is defined as the time-weighted average airborne
concentration of a particular substance when calculated over a normal 8-hour
work day, for a five-day working week.
(source:
http://www.nohsc.gov.au/ohsinformation/databases/exposurestandards/az/acetic_acid.htm)
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