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
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.