The APT process

Invented by David W. Spencer (aka Dave Spencer) for the movie The Black Cauldron, the APT (Animation Photo Transfer) process was a new breakthrough in how to transfer the animators' art onto cels. Compared to Xerography, it looked visually better. Basically, the process was a modification of a repro-photographic process; the artists' work were photographed on high-contrast "litho" film, and the image on the resulting negative was then transferred to a cel covered with a layer of light sensitive dye by making a "sandwich" of the negative and the cel and expose the negative to light. The layer of dye was sandwiched between the other two elements and exposed to the light through the transparent areas of the negative. Because it was actually divided into thinner layers of dye, each in a different color and sensitive to a specific wavelength of light, it was exposed to the relevant wavelengths one at the time. The light caused it to harden and fuse to the surface of the cel, and chemicals were then used to remove the unexposed portion, leaving the drawings in a variety of colors (photo emulsion). Small and delicate details were still inked by hand if needed. Spencer received a Technical award from the Motion Picture Academy for developing this process.