Acetate film was created around 1910 as a safer, less-flammable, alternative to nitrate. In a similar fashion to nitrate, it is created by dissolving cellulose in an acid but an acetic rather than nitric acid. The first iterations of the acetate base were very fragile and tended to decompose quickly (cellulose diacetate). This characteristic kept nitrate as the primary film base for 35mm. During the 1930s, manufacturers developed stronger compositions of acetate (cellulose acetate propionate and cellulose acetate butyrate) until finally settling on cellulose triacetate in the 1940s, the strongest of the acetate family. 16mm and 8mm films, being designed for the home and amateur filmmakers, were created only on acetate “safety film” bases.
However, each family member still has something in common: the process of acetate decomposition. Like nitric acid, acetic acid is also affected by the process of hydrolysis (chemical bonds breaking down with the introduction of water or humidity). Acetic acid is chemically identical to vinegar, so when the acid begins to separate from the cellulose, it emits vinegar smell, leading archivists and preservationists to refer to the process as “vinegar syndrome”. Film preservationists have also identified this process in a few general steps:
- The film starts to smell like vinegar and the base begins to soften.
- The film begins to shrink, and early stages of warping occur.
- The film starts to become stiff as the acetic acid continues moving out of the base. Warping such as buckling or edge wave occurs.
- The emulsion and base shrink at different rates, causing them to separate and emulsion may crack and flake off. Warped film continues curling and spoking.
- White powder (not mold) appears along the surface and edges of the film. Roll of film can solidify into a solid mass.
(Reminder: Not all films in the Byrd film collection are in this condition. This week represents only a fraction of the total films, most of which are in good and preservable condition.)
(side note: I’m thinking of having a “penguin day” next week…)
(Another reminder: sources used for Decomp Week will be provided on Friday.)