Safety motion picture film (so called because it is not flammable like nitrate base film) was almost always made of cellulose acetate plastic. A key issue in preserving this type of film is controlling the form of decay known as "vinegar syndrome." More properly referred to as acetate film base degradation, vinegar syndrome is a very similar problem to nitrate base deterioration. Its causes are inherent in the chemical nature of the plastic and its progress very much depends on storage conditions.
The symptoms of vinegar syndrome are a pungent vinegar smell (hence the name), followed eventually by shrinkage, embrittlement, and buckling of the gelatin emulsion. Storage in warm and humid conditions greatly accelerates the onset of decay. Once it begins in earnest, the remaining life of the film is short because the process speeds up as it goes along. Early diagnosis and cold, moderately dry storage are the most effective defenses.
Testing for Vinegar Syndrome
A handy way to test film for the presence of vinegar syndrome is the use of A-D Strips, small strips of specially treated paper that change color to indicate the severity of degradation.
Under normal room conditions, the strips are placed inside a film can for a day or so; the colors of the strips are then compared to a color chart that is calibrated in stages of film deterioration. A-D Strips can detect vinegar syndrome before there is a noticeable vinegar odor. If a film is in advanced stages of vinegar syndrome, it needs cold/frozen storage or duplication in order to preserve it. A-D Strips won a Technical Achievement Award from the Academy of Motion Picture Arts and Sciences in 1997. They can be purchased from the Image Permanence Institute.
IPI Storage Guide for Acetate Film: Instructions for Using the Wheel, Graphs, and Tables. Rochester, NY: Image Permanence Institute, Rochester Institute of Technology, 1993.