If someone asked whether your old microfilm smells, would you be offended? Maybe. On the other hand, if you are concerned about the long term retention of your library's microfilm, it would be prudent to find out if it smells. Microfilm collections that contain acetate film likely suffer from what is called "vinegar syndrome". Cellulose acetate microfilm, produced between 1923 and 1970, was especially popular during the 1930's and 1940's. Thought to be a safe, nonflammable material that would last centuries, it was developed to replace nitrate based film, notorious for its flammability. Unfortunately for acetate film owners, longevity is not one of it's strong suits, and as it degrades it releases a vinegar smell.

Moisture is the culprit. Acetate film can't live without it and can't live with it. In order to remain supple and work properly, acetate film requires some amount of moisture. If the film is too dry it could break when handled or used in film readers. On the other hand, moisture in the acetate film reacts with the acetate ions contained within it to form acetic acid. As this chemical reaction occurs, the film base shrinks and the film becomes warped. Eventually it will be too warped to be useful. In highly humid environments acetate film will absorb more moisture and deterioration will occur more rapidly.

How might you know if you have acetate microfilm? The vinegar smell is one way, but don't breathe too deeply. The gas that is emitted from the film as it degrades is a health hazard. Although it's not clear what level of health hazard is involved, consider this: the occupational use of methylene chloride, an organic solvent used in the production of triacetate film base, is now closely regulated by OSHA as a suspected carcinogen. If the smell is not present, look at the edge of the film. Acetate film is dark along the edges as opposed to polyester film that is transparent. Acetate film also tears easily, whereas polyester does not. Libraries that own the U.S. Supreme Court briefs and records produced by the University of Chicago on microfilm during the 1930s and 1940s, have acetate film.

If you think that your library has acetate microfilm you can determine its acidity using a product called A-D strips. These paper strips were developed by the Image Permanence Institute for the purpose of detecting and measuring the extent of acetate film deterioration. The strips are placed inside closed containers of film where they will change color in the presence of acidic vapor. They provide to libraries the means for diagnosing not only the presence of acidity but also the level. As the concentration of acetic acid intensifies, the strips change from blue to green to yellow. The Academy of Motion Picture Arts and Sciences was so impressed with A-D strips that it honored the invention with one of its Technical Achievement Awards in 1997. A-D strips are available from IPI and preservation supply vendors, such as University Products.

Although the chemical reaction that produces "vinegar syndrome" cannot be stopped, proper storage can slow the degradation. If your acetate microfilm smells like vinegar but is not yet warped, there are things you can do to hinder the degradation process. First and foremost, the temperature and relative humidity (RH) of the storage area must be regulated. According to IPI, acetate film stored at room temperature and moderate RH will begin to deteriorate in 50 years. The lower the temperature, the longer the film will last. A cold environment, less than 50° F., is ideal, but not usually practical for high use collections. Cool temperatures, below 72° F., will also extend the life of acetate film. A cool, non-fluctuating temperature and a moderate RH (20% to 50%) will serve to lessen the rate of deterioration.

Since vinegar syndrome is autocatalytic, acetate film will last longer if it is allowed to breathe. Closing the film away in containers that do not allow the gases to escape leaves the film to stew in its own juices and shortens its life. While this may seem easy to accomplish, it is complicated by the need to protect people and other film. If the acetate film is allowed to breathe, it should be stored in a well-ventilated area and away from healthy, non-acetate film. While it is not clear whether healthy film is in grave danger if stored near acidic film, it is best to be safe and segregate them. Containers should also be chemically inert. Some preservationists recommend using MicroChamberŽ enclosures, a product containing zeolite molecular traps that absorb pollutants.

In 1938, prior to the 1939-40 New York World's Fair, Westinghouse buried a 5000 year time capsule. Much of the capsule contains newspapers and books reproduced on the best microfilm technology could offer at that time, acetate based microfilm. It's a safe bet that when the capsule is opened it will not reveal as much about the early 20th century as was intended.

For more information about vinegar syndrome, there are two good articles in American Cinematographer, June 1996: Attack of the Vinegar Syndrome, and Film Preservation: A Practical Guide. The first is also on the web at: http://capital.net/com/jaytp/VINEGAR.HTM.

For general information on proper storage of microforms see section 5, leaflet 1 of the NEDCC's Preservation of Library and Archival Materials: A Manual at: http://www.nedcc.org/plam3/tleaf51.htm.