Film Assessment, Part 1: Smells Like Vinegar

One of the many activities Preservation Services performs for the library's collections is condition assessment of films. We have a large number of films in a variety of formats in the collections, and assessing them is important for several reasons:

1. For use. Sometimes patrons, scholars, or alumni want to view our old films. Of course we would love to support viewing of the films, but they aren’t always in good enough condition to be viewed on a projector.
2. For reformatting. People often want to use clips from our film footage for other purposes. We also sometimes reformat film as part of the film preservation process, to allow people to easily view the content in a digital format.
3. For accessioning. When we receive new (or new-to-us) films into the collection, a physical assessment is an important first step in determining how to best store and manage the items.

Why is film condition assessment important? Well, films have some unique physical qualities that make them degrade in characteristic ways, often much faster than books and paper. The National Film Preservation Foundation has an excellent book on film preservation, which can be downloaded as a PDF for free.

To sum up the basic issue, film is made of three parts: the image, which sits on an emulsion layer, which sits on a plastic base, and the type of plastic used for the base determines how it will degrade. Modern film bases are made of stable polyester, but historic film bases were made of either cellulose acetate or, originally, cellulose nitrate. Cellulose nitrate was used in the late 19th and early 20th centuries and is extremely dangerous because when it degrades it is highly flammable.

Cellulose acetate or "safety film" replaced cellulose nitrate in the mid-20th century and, while not dangerous like nitrate film, it does decay in a way that causes irreparable damage to the film. The chemical process of decay turns the acetate into acetic acid (the acid in vinegar), which causes the film to shrink, warp, and turn brittle. It also emits a characteristic odor of vinegar, which is a sure sign that the film is decaying.

The best way to slow film decay is to store films in good-quality containers in very cold, relatively dry environments. Films can also be digitized, transferred to a stable base, and made accessible using DVDs to prevent decay and damage from use.

In a future post, I’ll talk more about the actual process of condition assessment. Stay tuned!

Written by Helen Bailey.