cel

thumb|Painting with acrylic paint on the reverse side of an already inked cel.

A cel, short for celluloid, is a transparent sheet on which objects are drawn or painted for traditional, classical, hand-drawn animation. Actual celluloid (consisting of cellulose nitrate and camphor) was used during the first half of the 20th century. Since it was flammable and dimensionally unstable, celluloid was largely replaced by cellulose acetate (cellulose diacetate and cellulose triacetate) and polyester. With the advent of computer-assisted animation production (also known as digital ink and paint), the use of cels has become obsolete in major productions. Walt Disney Animation Studios stopped using cels in 1990, when Computer Animation Production System (CAPS) replaced this element in their animation process. In the next decade and a half, other animation studios phased cels out as well in favor of digital ink and paint.