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Condition Assessment
Condition Assessment
A variety of methods exist for evaluating the condition of
cellulose acetate. These are methods which involve taking a single reading as
well as methods for monitoring material while in storage.
An understanding of the degradation mechanisms of cellulose
acetate is vital to an evaluation of the condition of the material. A brief
outline of degradation processes is given in Appendix
4.
Evaluating the Stage of Deterioration of Cellulose Acetate
The generation of acid is the first and most sensitive
indicator of acetate base degradation (Bigourdan et al., 2000).
Before the 'autocatalytic point' (see Appendix 4), cellulose
acetate shows little or no signs of degradation. Once past this point,
degradation can be rapid and severe. Therefore, the 'stages of deterioration'
of cellulose acetate apply mainly to film that has already passed the
autocatalytic point. It is only these later stages that are easily determined.
If a film is showing marked signs of deterioration, such as
edge curl or plasticiser bubbles, it is certainly in the late stages of
deterioration and must be dealt with promptly. However, film that shows no
signs of deterioration and does not emit a vinegar smell may still be quite
deteriorated.
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It is difficult to evaluate the extent of
deterioration of cellulose acetate film. Films that do not exhibit signs of
deterioration, such as vinegar odour, edge curl or plasticiser bubbles, may
still be quite degraded. |
Film degradation is highly dependent on factors such as
manufacture and history, making it difficult to predict how any given film will
behave. For example, it is not unlikely for a young film to degrade more
rapidly than an older one if it has been subjected to less-favourable
conditions.
The IPI Storage Guide for Acetate Film is a
"tool for evaluating and planning storage environments for acetate base
photographic film, cinema film, and microfilms" (Reilly, 1993, p.2) The
IPI Storage Guide is useful as a tool for assessing the likely life
expectancy of fresh and deteriorated film under various environmental
conditions 2.
The best strategy when dealing with cellulose acetate
collections is to treat the preservation of severely degraded but salvageable
material as a matter of urgency, and then to treat all other cellulose acetate
films as 'suspicious' and requiring preservation attention as soon as
possible.
Monitoring Deterioration in Storage
There are several available methods for monitoring the
extent of degradation within a cellulose acetate collection (eg IPI A-D (Acid
Detection) strips, Dancan's Danchek strips or buttons, M-Check or Film Decay
Detectors (FDD)). Most passive methods involve the use of an acid/base
indicator which changes colour on exposure to acid vapours. Methods vary in
their uses and response times. Activated carbon may also be used to analyse
vault air.
A-D Strips were developed by the Image Permanence Institute
(IPI) in Rochester, New York. They are useful in gaining an idea of the stage
of deterioration of acetate materials. They operate by measuring the amount of
acid produced by the collection item in a closed environment. Using the strips,
the stage of deterioration can be roughly estimated within a couple of days.
A-D Strips, and instructions for their use, are available
from IPI. 2 At the time of writing, they cost US$27.00 or US$45.00
per package, depending on how many packages are ordered at a time. Each package
contains 250 strips. If the bag is properly sealed and stored, A-D strips can
last for years.
While relatively inexpensive to purchase, A-D strips may be
time consuming to place in enclosures and retrieve and record results.
Individual collection items require a closed environment and a period of at
least one day before the test results can be read. In cold storage it can take
up to 5 days to get a final reading.
Some organisations use A-D Strips to record acetic acid
levels on a monthly basis, and/or to check the condition of material entering
their collection.
Other indicators which are commercially available include
'Dancan's Danchek' (http://www.dancan.dk/).
Edge states that "archivists may require more than one type
of indicator"; one that works rapidly for checking film as it goes into / comes
out of storage, and one that may be on-going inside the vault (Edge, 1995).
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Whether or not monitors are used, it is recommended
that random survey-type checking of cellulose acetate collections be carried
out at least every two years. |
(2) Available from: Image Permanence
Institute, Rochester Institute of Technology, 70 Lomb Memorial Drive, Rochester
NY 14623-5604 http://www.rit.edu/~661www1/sub_pages/frameset2.html. Ph: 716 475
5199 Fax: 716 475 7230
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