Saving the Museum's Microfilm Collection: Duplication and Preservation

The National Air and Space Museum Archives Division is the custodian of thousands of reels of microfilm of historic documents – engineering drawings of US aircraft like the P-51 Mustang and the F4U Corsair, individual aircraft history cards, and technical documents captured by the Allies at the end of World War II. The information contained in these reels is used on a daily basis by the museum's curators and by our aircraft restoration specialists. It's also in frequent use by scholars, historians, and by the general public – many historic aircraft restoration projects use duplicate microfilm from the Archives' collection.

But this historic collection, much of it now over fifty years old, is rapidly deteriorating due to the nature of the materials used in its manufacture and in the way the microfilm was originally processed. In the near future, much of our microfilm collection will become unusable, and the irreplaceable information it contains – much of it available no where else - will be lost.

What's Happening to Our Microfilm?

Microfilm – all film – is a sandwich of an emulsion (which contains the image), a support layer, and a binder to hold the emulsion and support together:

When the photographic industry began to look for a support layer that would be more convenient than the cumbersome glass plates that formed the staple of 19th photography, it first turned to cellulose nitrate, a flexible plastic material. Unfortunately, cellulose nitrate is also highly flammable and after a number of spectacular (and fatal) fires the industry began searching for a safer support. In the early 1920s, the industry developed cellulose acetate-based films, which it marketed as "safety film," and which continue as the standard support for film available for retail sale to this day.

Although acetate-based films do not have the spectacular drawback of nitrate films, neither are they stable in the long term. As the film ages the acetate compounds break down and release acetic acid vapor, giving the film a vinegar smell and giving the process its popular name: "vinegar syndrome." The transparent support layer shrinks. Since the emulsion and binder do not shrink, the film curls away from the emulsion and, in time, the binder may fail causing the emulsion to bubble off of the support. At the same time, the support yellows and becomes brittle, so that attempts to flatten the film can cause it to break. The rate of deterioration varies with the actual chemical composition of the support and the storage conditions, but the deterioration is irreversible. In time, all our acetate-based film will deteriorate to the point where it will be unusable. Although manufacturers have developed chemical baths to soften deteriorated films, a film can only be treated once for remastering, after which the film is no longer usable.

What Are We Doing About It?

The development of polyester-based films in the 1960s provides a stable medium for photographic materials. Current estimates place the usable life span of polyester film in the hundreds of years, leading archivist to consider polyester film as the standard preservation medium. As our budget allows, we're remastering our nitrate- and acetate- microfilms onto stable polyester film stock before they reach the point of no return. Unfortunately, as we have thousands of rolls of microfilm and only limited funding, this project is expected to take years, during which time most of the microfilm collections will be held in cold storage (to slow the deterioration as much as possible) and monitored. In practical terms, this means access to much of the microfilm collections will require a minimum of 24 hours notice, as the film must be warmed to room temperature before use.

Why Not Digitize It All?

While digitization of the microfilm provides convenient access to the information, it is not an acceptable method for the long-term preservation of the material. By remastering the microfilm we make possible the continued digitization of portions of the collection; if we simply digitized the collection without creating new microfilm masters, we run the very real risk of losing access to the data due to the rapid changes in digital technology. The NASM Archives uses digital technology to provide access to a variety of our collections, but for long-term preservation we rely upon hard copy - whether on paper or film.

To help defray the expenses of the microfilm rescue project, we have had to increase the price we charge for duplicate microfilm from $25.00 to $30.00 per reel. To those that make use of Archives Division microfilm, we hope that the satisfaction of helping us save our historic collection for posterity will offset, somewhat, the inconvenience of the increased costs. Thank you for your continued support and understanding.