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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.

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).

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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