Cromalin, introduced in 1972, is the most popular color proofing system in use today. Color proofing in the printing business means checking the accuracy of color during the process of reproducing an artist's drawing, or photograph on the printed page. Proofing is necessary partly because errors can occur in the process, and partly because color itself is the complex product of an almost infinite combination of the three primary colors: red, yellow and blue.
In the typical "four color" printing process, colors are made by combining magenta (a reddish color), yellow, cyan (a bluish color) and black. Prior to photopolymer proofing technologies like Cromalin, high-quality color proofing meant superimposing layers of color-sensitive films on expensive printing plates. If the colors didn't turn out right, the process would have to be repeated, sometimes several times. Cromalin polymer laminates are more efficient and accurate, so final colors are more likely to look right on the first try.
Cromalin uses light-sensitive photopolymers laminated to paper stock to register either positive or negative film images. Light-exposed areas harden leaving sticky surfaces when the laminate's cover sheet is removed. Dyed powder, or toner, is applied and adheres to the sticky portions. Additional cover sheets are applied and removed, and different toners used on successively exposed sticky surfaces, until the desired color results have been achieved. In 1981 DuPont introduced an automatic toning machine to perform these functions automatically. More recently, DuPont has developed Cromalin products for computer-based digital publishing and inkjet printing. These "computer-to-plate" technologies supplement the traditional line of Cromalin "film-to-plate" products.