Once the clean-ups and in-between drawings for a sequence are completed, they are prepared for photography, a process known as ink-and-paint. Each drawing is then transferred from paper to a thin, clear sheet of plastic called a cel, a contraction of the material name celluloid (the original flammable cellulose nitrate was later replaced with the more stable cellulose acetate). The outline of the drawing is inked or photocopied onto the cel, and gouache, acrylic or a similar type of paint is used on the reverse sides of the cels to add colors in the appropriate shades. In many cases, characters will have more than one color palette assigned to them; the usage of each one depends upon the mood and lighting of each scene. The transparent quality of the cel allows for each character or object in a frame to be animated on different cels, as the cel of one character can be seen underneath the cel of another; and the opaque background will be seen beneath all of the cels.
http://en.wikipedia.org/wiki/Traditional_animation

Художник-контуровщик — художник, задачей которого является перенос рисунка с бумаги на целлулиодную плёнку[2].
http://ru.wikipedia.org/wiki/Художник-мультипликатор