cel

Cel, in the context of animation, refers to a transparent sheet made of cellulose-based material (originally nitrocellulose, later safer forms such as acetate or Mylar) on which drawings are created for each frame of a traditional hand-drawn sequence. The term derives from the cellulose-based sheets used in the early animation industry and became a standard term for the layered cels used in production.

Historically, cel animation emerged in the early 20th century and became the dominant technique for producing 2D animated films. A typical setup involved drawing ink lines on the front of a clear cel, painting colors on the reverse, and placing a painted background on a separate sheet. By layering multiple cels with different elements (foreground characters, midground action, and background scenery), studios could animate complex scenes with relatively reusable elements. This method allowed for multiple frames of movement to be photographed in sequence to create motion.

In practice, each frame required a new or adjusted cel, with accuracy in alignment (registration) between layers crucial for the illusion of fluid motion. The cel process enabled efficient production and the ability to reuse backgrounds or parts of figures. Beginning in the late 20th century, advances in digital imaging and compositing reduced reliance on physical cels, leading to a decline in their use for new productions. However, original animation cels remain valuable collectibles and historical artifacts, preserved by museums, studios, and collectors for their artistry and connection to classic animation.

The term cel is primarily associated with traditional animation, though the concept of layered transparency persists in modern digital workflows, which simulate the same principle without physical sheets.