As an emerging conservator, sometimes I find it difficult to describe to others what I do. When many people hear the word conservation, they immediately think of people protecting wildlife.
The Public Library of Cincinnati and Hamilton County has a wonderful collection of materials about the use of the Ohio and Mississippi rivers known as the Inland Rivers Collection. Recently a group of photographs with accompanying film negatives from this collection came to the Lab.
What for? Well, film has been made using different chemicals over the years, some of which are very unstable. The Lab’s task was to divide and house the entire grouping according to film type. Special attention was given to identifying any cellulose nitrate negatives and isolating them in separate storage housing with the recommendation they be digitized and then disposed of in accordance with Ohio’s guidelines for discarding hazardous materials.
Cellulose nitrate film was the first widely used flexible plastic film. In the late nineteenth century it supplanted heavy, fragile glass plates. Great! Except nitrate is also a chemical component in gunpowder. As cellulose nitrate film degrades it goes through several distinct stages, beginning with silver mirroring and yellowing. Then it may become sticky and smelly (nitric acid odor). Gradually the negative changes to an amber color with the image beginning to fade. Eventually the negative can soften to a point where it may stick to adjacent pictures or its enclosure. In the final stage it turns to a brown acidic powder. As deterioration progresses it accelerates and in the last stages the film may begin to generate its own heat and ignite. A cellulose nitrate fire doesn’t need oxygen to burn so most of the usual firefighting methods won’t put it out. Any grouping of cellulose nitrate film increases the risk. Reels of motion picture film contained in metal canisters concentrate the off-gassing and accelerate the deterioration process.