collotype

collotype, photomechanical printing process that gives accurate reproduction because no halftone screen is employed to break the images into dots. In the process, a plate (aluminum, glass, cellophane, etc.) is coated with a light-sensitive gelatin solution and exposed to light through a photographic negative. The gelatin is hardened in exposed areas and is then soaked in glycerin, which is absorbed most in the non-hardened areas. When exposed to high humidity, these areas absorb moisture and repel the greasy ink. The hardened areas accept the ink, and the plate can be used to print a few thousand copies of the positive image.