The Cause of the Vinegar Syndrome
by Image Permanence Instute
Selections from the Storage Guide
written by James M. Reilly in 1993

It is useful to understand the progression of acetate deterioration so that the condition of a film collection can be assessed more knowledgeably. Of all the changes brought about by degradation, the first sign is usually the vinegar odor. The figure shows how acidity builds up in film base over time. It is the shape of this curve that is important, because it describes how acidity is at first almost nonexistent, then for a long time builds up gradually. Then, after the acid level increases to a certain point the increase suddenly becomes very rapid. Before this point, acidity rises slowly. After it, large of amounts of acid are generated in a very short time.

The reason why degradation follows this course is easy to understand. Acetic acid is formed when the acetyl “side groups” are split off from the cellulose molecules. There are three factors that induce such changes: heat, moisture and acid. In the early stages there is little acid present so the reaction rate is determined primarily by heat and moisture. During this long, slow buildup, the storage environment plays the decisive role. The temperature of the storage room determines how much heat energy is available to push deterioration along.

The sharp bend in the time-vs. acidity curve represents the point when acidity becomes another major factor, along with heat and moisture, in determining the rate of deterioration. The more advanced the deterioration becomes, the more the reaction rate is influenced by the presence of acidity. The reason is that the reaction is now “feeding on itself” – displaying what scientists call autocatalytic behavior. A catalyst is a substance that speeds up a chemical reaction but is not consumed by it. The whole process snowballs.

IPI Storage Guide for Acetate film by
Image Permanence Institute
Rochester Institute of Technology
70 Lomb Memorial Drive
NY 14623-5604
Phone 716 475 5199 – Fax 716-475 7230