Cel Painting
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Cel - Short for "celluloid," the term refers to the clear sheets of celluloid on which animated characters were traced from the animators' cleaned up pencil drawings, painted, and then photographed on top of a background. Cels were made of nitrate cellulose until 1940, then cellulose acetate in later years. With 24 frames per second of film, there could be as many as 24 cels per second, but normally, cels were held for two frames. Thus a film like "Snow White" might have as many as 60,000 cels. The use of cels ceased in the late 1980s as computers were adapted to accomplish the same task.