What's That Smell??!!
Safety motion picture film (so-called because it is not flammable like nitrate base film) is 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 vinegar syndrome. Once it begins in earnest, the remaining life of the film is short because the decay process speeds up as it goes along. Early diagnosis, proper restoration and cool-and-dry storage with molecular sieves are the most effective defenses against vinegar syndrome.
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