Vinegar syndrome, also known as acetic acid syndrome, is a condition created by the deacetylation of cellulose acetates (usually cellulose diacetate) and cellulose triacetate. This deacetylation produces acetic acid, giving off a vinegar odor that gives the condition its name; as well, objects undergoing vinegar syndrome often shrink, become brittle, and form crystals on their surface due to the migration of plasticizers. Vinegar syndrome widely affects cellulose acetate film as used in photography. It has also been observed to affect older magnetic tape, where cellulose acetate is used as a base, as well as polarizers used in liquid-crystal display units and everyday plastics such as containers and tableware. High temperatures and fluctuations in relative humidity have been observed to accelerate the process. The process is autocatalytic, and the damage done by vinegar syndrome is irreversible.

History

The first instance of cellulose triacetate degradation was reported to the Eastman Kodak Company within a decade of its introduction in 1948. The first report came from the Government of India, whose film materials were stored in hot, humid conditions. It was followed by further reports of degradation from collections stored in similar conditions. These observations resulted in continuing studies in the Kodak laboratories during the 1960s. Film degradation can only be delayed by storage in dry and cold conditions. It was initially thought that storage under recommended conditions might delay decay by 450 years, but some films are developing vinegar syndrome after just 70 years of cold dry storage. The film preservationist Harold Brown is credited with coining the phrase "vinegar syndrome".

The progression of degradation

In acetate film, acetyl (CH3CO) groups are attached to long molecular chains of cellulose. With exposure to moisture, heat, or acids, these acetyl groups break from their molecular bonds and acetic acid is released. While the acid is initially released inside the plastic, it gradually diffuses to the surface, causing a characteristic vinegary smell. The decay process follows this pattern:

Testing

A testing product developed by the Image Permanence Institute, A-D, or "acid-detection" indicator strips change color from blue through shades of green to yellow with increasing exposure to acid. According to the test User's Guide, they were "created to aid in the preservation of collections of photographic film, including sheet and roll films, cinema film, and microfilm. They provide a nondestructive method of determining the extent of vinegar syndrome in film collections." These tools can be used to determine the extent of damage to a film collection and which steps should be taken to prolong their usability.