Film Base - Acetate

Acetate

Despite the dangers of the nitrate film base being known practically since its development, it was used in virtually all major motion pictures prior to 1952, when Kodak completed a four year conversion program to the sole manufacturing of acetate base film stocks. Kodak began working with acetate "safety film" as early as 1909, and started selling it in 1910 for 22 mm film. Acetate has always been used with 8 mm and 16 mm formats, as they were originally created for amateur home movie usage, and generally was used for most sub-35 mm formats to minimize risk to the general public. (Several formats, such as 17.5 mm, which were often re-slit from 35 mm were nitrate, however. One of Kodak's reasons for choosing 16 mm instead of 17.5 mm for a standard amateur format width was specifically to prevent nitrate re-slits from being used in home movies.) All motion picture camera negatives are now shot on acetate film because it is safer than nitrate but not as strong as polyester bases, which may damage the camera rather than the film should a jam occur. Acetate can also be spliced with film cement, while polyester can only be spliced with tape or an ultrasonic splicer, so polyester would be hard to edit. Acetate film does not burn under intense heat, but rather melts, causing a bubbling burn-out effect - this can be seen simulated in films such as Persona (1966) or Velvet Goldmine, or, if one is unlucky, in real life during a film screening when a frame becomes stuck in the projector's film gate. Acetate films are also subject to degradation over time. With exposure to heat, moisture or acids the acetyl groups which are attached to long chains of cellulose which form the film base are broken from their molecular bonds and free acetic acid is released with a characteristic smell of vinegar. This is known as vinegar syndrome. As the degradation progresses the film base becomes brittle and shrinks.