Tech Tips for Archivists:
Ten Steps to Control Vinegar Syndrome
By Reed Bovee, Chief Technology Officer, Reflex Technologies
When you open a can of archival film and smell ‘vinegar’, you’re smelling the cellulose acetate film base decomposing.
The vinegar smell doesn’t mean the film has significantly deteriorated, but it does mean acetic acid is leaching out of the film base and the breakdown has begun. Chemical degradation of film base is an irreversible process.
Acetate base – safety film – was commercialized in the late 1940’s and early 1950’s when it replaced unstable (flammable) nitrate base. It took scientists another 30 years to understand that acetate film is also unstable.
This is really an acetate base problem, but the acid also can react with the gelatin in the image layers and the dyes (in color film) causing the emulsion to soften and the image to deteriorate.
Vinegar syndrome can cause ‘cloudiness’ on the image, much of which, surprisingly, can be cleaned off. When you follow recommended film cleaning procedures, the white powdery material can be removed and the odor becomes less pronounced.
Over time, vinegar syndrome can also make film sticky – so when you unwind it, one layer can adhere to the next resulting in defects such as ferrotyping. In severe cases, it can pull bits of the emulsion off the base.
The film can also shrink – and at different rates — more at the outer edges and less in the center. The result is a kind of buckling effect, with the individual frames becoming somewhat cupped or curved.
But what eventually happens is – the film becomes increasingly brittle, to the point where it can’t be handled, and finally you open up the can and it’s just powder.
While freshly-processed acetate film put immediately into cold storage can last hundreds of years, most films are not handled that way. In typical ‘real world’ storage conditions, vinegar syndrome can start after only a few years – and it can’t be stopped.
But, it can be slowed down. Here are ten steps you can take to minimize its effects:
Open the can and look at the condition of the film. Film in rusted cans should be repackaged in clean archival packaging.
Remove films from metal reels with spokes. Over time, vinegar syndrome will cause metal reels to rust and film to shrink and twist, which will make it more difficult to remove from ‘spoked’ reels without edge damage.
Rewind them on plastic cores. (www.kodak.com/motion) A lab core with a 3-inch diameter helps to ‘relax’ the film. Machine-winding – with proper alignment and even tension — is recommended.
Put an A-D strip (www.imagepermanenceinstitute.org) in the can, even if you don’t smell vinegar. The strip absorbs acetic acid and its color scale quantifies the level of film degradation from blue (minimal) to bright yellow (advanced decomposition).
Put desiccants — such as molecular sieves (www.kodak.com/motion) — in the can to absorb moisture and contain vapors. The Kodak site provides guidance for the number of sieves to be used, based on size of the reel.
Lay the film cans flat – never on their vertical edge – and no more than twelve inches high.
Store the film in a cold, dry environment. Storage in an environment with a temperature of 45° to 50°F (7° to 10°C) and no more than 20- to 30-percent relative humidity can significantly improve film’s stability. Films with advancing vinegar syndrome can be stabilized and decay can be postponed by storage in subfreezing temperatures.
Inspect the films at least every few years. Look for physical changes in condition, check the A-D strip for color changes, and replace the desiccants, which don’t last indefinitely. Increase the inspection frequency if any vinegar odor or film deterioration is observed.
Wear white cotton gloves when inspecting archival films. Wearing cotton gloves prevents skin oils or any other contaminants from transferring to the film and also protects the inspector’s hands.
And, if possible, separate the films in different stages of decay. Try to keep as much physical distance as possible between cans with vinegar syndrome and those without. Unfortunately, the syndrome is contagious; cans stored together can advance degradation in all.
So, the bad news is: most archival film is on acetate base – which means most archives are affected by vinegar syndrome. But the good news is: by taking a few basic steps and maintaining proper storage conditions, archivists can extend the life of acetate films – even those starting to deteriorate – for a long time.
Reprinted by permission of the Society of American Archivists. This article originally appeared in Archival Outlook (Jan./Feb. 2013).