Safety film

Cellulose acetate film, or safety film, is used in photography as a base material for photographic emulsions. It was introduced in the early 20th century by film manufacturers as a safe film base replacement for unstable and highly flammable nitrate film.

Cellulose diacetate film was first created by the German chemists Arthur Eichengrün and Theodore Becker, who patented it under the name Cellit, from a process they devised in 1901 for the direct acetylation of cellulose at a low temperature to prevent its degradation, which permitted the degree of acetylation to be controlled, thereby avoiding total conversion to its triacetate. Cellit was a stable, non-brittle cellulose acetate polymer that could be dissolved in acetone for further processing. A cellulose diacetate film more readily dissolved in acetone was developed by the American chemist George Miles in 1904. Mile's process (partially hydrolysing the polymer) was employed commercially for photographic film in 1909 by Eastman Kodak and the Pathé Fréres. Starting with cellulose diacetate, this innovation continued with cellulose acetate propionate and cellulose acetate butyrate in the 1930s, and finally in the late 1940s, cellulose triacetate was introduced, alongside polyester bases. These less flammable substitutes for nitrate film were called safety film.

The motion picture industry continued to use cellulose nitrate supports until the introduction of cellulose triacetate in 1948, which met the rigorous safety and performance standards set by the cinematographic industry. The chemical instability of cellulose nitrate material, unrecognized at the time of its introduction, has since become a major threat for film collections.

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