Vinegar Syndrome is a term used in the industry to describe decaying film. It is called this because of the vinegar like odor that decaying film gives off during the decaying process.
To understand what Vinegar Syndrome is, we have to understand exactly what film is made from. Modern films, those made after 1948, are made from a film stock base containing Cellulose Triacetate. Triacetate is a polymer, manufactured from a chemical reaction involving cellulose and acetic acid. Vinegar syndrome is the reverse reaction of the breakdown of the acetate.
Because of the way the film substrate is made, there will always be an inherent amount of ‘free’ acetic acid, generally trapped between the substrate and the emulsion. This is normal, and under cool conditions of storage, around 50 degrees Fahrenheit, Vinegar Syndrome may never make an appearance.
The trouble really begins with heat and high humidity. These cause the film to start breaking down into the two main substances that formed the base material in the first place, i.e. cellulose and acetic acid.
The area of the film that seems to be the most affected is between the substrate and emulsion. A build-up of humidity, combined with heat will cause acetic acid to burst through the emulsion as a gaseous substance, creating microscopically small holes through the emulsion as it escapes into the air and gives us the typical vinegar odor that exudes from acetic acid.
The decay process follows this pattern:
- Acetic acid is released during the initial acetate base deterioration, leading to the characteristic vinegar odor. This signal marks the progression of deterioration.
- The plastic film base becomes brittle. This occurs in the advanced stages of deterioration, weakening the film and causing it to shatter with the slightest tension. These physical changes happen because cellulose acetate consists of long chains of repeating units, or polymers. When the acetic acid is released as these groups break off, the acidic environment helps to break the links between units, shortening the polymer chains and leading to brittleness.
- Shrinkage also occurs during this process. With the cellulose acetate polymer chains breaking into smaller pieces, and with their side groups splitting off, the plastic film begins to shrink. In advanced stages of deterioration, shrinkage can be as much as 10%.
- As the acetate base shrinks, the gelatin emulsion of the film does not shrink, because it is not undergoing deterioration. The emulsion and film base separate, causing buckling, referred to by archivists as ‘channeling.’ Sheet films are often severely channeled in the later stages of degradation.
- Crystalline deposits or liquid-filled bubbles appear on the emulsion. These are evidence of plasticizers, additives to the plastic base, becoming incompatible with the film base and oozing out on the surface. This discharge of plasticizers is a sign of advanced degradation.
- In some cases, pink or blue colors appear in some sheet films. This is caused by annihilation dyes, which are normally colorless and incorporated into the gelatin layer. When acetic acid is formed during deterioration, the acidic environment causes the dyes to return to their original pink or blue color.
Can it be treated?
Unfortunately there is currently no practical way of halting or reversing the course of the degradation once it has begun.
Can you transfer my films that have Vinegar Syndrome?
Depending on the stages of deterioration, we may still be able to transfer your affected reels. Unfortunately, the warping associated with the deterioration may affect the picture quality. Also, once un-spooled from the tightly wound original reel, we may not be able to return the reel back to the original reel in the same tightly-wound manner and we generally only get one chance to transfer the reel. (That’s the good news. The bad news is that if you don’t act soon – you may never get a chance to preserve these reels.) It is also important to note that studies show that Vinegar Syndrome is contagious, so you should check all of your reels and separate out the ones that have been affected from the ones that appear fine. You should consider preserving all of your reels as soon as possible as once the odor is apparent, there is no way to reverse the process.