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Inherent Vice: Film Supports

Acetate Film

Cellulose acetate film was first invented in the late 19th century to replace cellulose nitrate film, which was already recognized for its dangerous flammability. However, the first acetate was not practical for use. Acetate is an umbrella term that encompasses several different types of film: cellulose diacetate, acetate propionate, acetate butyrate, and cellulose triacetate. Cellulose diacetate was developed first and was used for both sheet and roll film between 1923 and 1955, but it had a tendency to shrink a great deal.

Acetate butyrate and propionate films were developed during the 1940s as alternatives to cellulose diacetate; these were used for home movie roll film, x-ray film, sheet film, and aerial film. Nitrate was still superior to these films, however, for 35mm motion picture film.

Cellulose triacetate was developed in the late 1940s. It was used for sheet film, various sizes of roll film (particularly 8mm and 16mm, which are commonly found in cultural collections), and motion picture film. It is still used today for most types of roll film, including transparency film (slide film). During the 1970s, however, polyester film began to replace it for sheet film.

Characteristic Types of Deterioration

While cellulose acetate films do not have a problem with flammability, they are just as chemically unstable as nitrate films. The hydrolysis of acetate is referred to as "vinegar syndrome" due to the distinctive vinegar odor it produces. Vinegar syndrome proceeds quickly at room temperature, and it is accelerated by higher temperature and relative humidity. The stages of deterioration are:

This acetate negative, in the last stage of deterioration (Stage 6), shows channeling where the emulsion has separated from its base.

1. No deterioration.
2. The film gives off a vinegar odor (due to acetic acid) and begins to become brittle and shrink.
3. The film begins to curl and may have blue or pink staining.
4. The film loses flexibility and warps.
5. The film develops liquid-filled bubbles and crystalline deposits, sometimes obscuring the image.
6. As the film base continues to shrink, the emulsion becomes separated from the base in some areas, known as channeling.

The deterioration of cellulose acetate is autocatalytic, meaning that as the film becomes more acidic, this acidity further accelerates the deterioration process. Cold or frozen storage is recommended to slow deterioration. The Image Permanence Institute (IPI) has developed a product called A-D Strips that can be used to determine the extent of chemical deterioration in acetate films; see IPI's A-D Strips Web page for more information.

Identifying Acetate Film

If film exhibits the characteristic forms of deterioration described above, it can be easily identified as acetate film. Other methods for identifying acetate film are similar to those for nitrate film: dating, edge printing (acetate film is usually marked as "SAFETY" to differentiate it from nitrate film), notch codes, and destructive tests (the flotation and burn tests). Polyester roll film may also be marked as "SAFETY." When held up to the light and viewed edge-on, however, acetate roll film transmits very little light compared to polyester roll film.