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Identification of cellulose acetate in collections
Identification of cellulose acetate in collections
The identification of cellulose acetate within collections
is a first step in planning how to manage this material. A range of formats in
Australian collections are on cellulose acetate. These include: sound material,
motion picture film, microfilm, photographic negatives, and microfiche, and may
include other less common formats such as graphic arts films and overlay
transparencies.
Although this Guide is limited to identifying documentary
based formats, it is worth noting that cellulose acetate was used for a wide
range of collection items including dice, casino chips, glasses frames, and
imitation tortoiseshell goods. These are all subject to the same type of
degradation and should be cared for appropriately.
Film Collections
Film base materials for motion picture film, microfilm,
microfiche and photographic negatives are often difficult to differentiate from
each other. All films in their undeteriorated state tend to fulfil the basic
requirements of being clear and flexible, and identification of the major
polymer involved can be complex.
While a variety of film bases have been used throughout the
past century, only three of these form the major part of most collections. They
are:
- cellulose nitrate;
- cellulose acetate; and
- poly (ethylene terephthalate) (commonly referred to
simply as 'polyester').
Other bases, such as polycarbonate and polystyrene, were
never used to any great extent and are quite rare. The cellulose acetate
category encompasses the mixed esters of cellulose acetate butyrate and
cellulose acetate propionate as well as cellulose diacetate and triacetate. All
the acetates have similar deterioration characteristics and preservation
requirements, and can be considered as a group.
The following sections will provide a practical guide to the
steps necessary for the identification of film within collections.
Sound collections
In the case of sound collections, the principal materials
used for the base are cellulose acetate, polyvinyl chloride (PVC) and
polyester. (Polyvinyl chloride is another unstable carrier, which releases
hydrochloric acid as it deteriorates). So called 'Acetate Discs' are really
based on a modified nitro-cellulose compound, and are not cellulose acetate.
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