diazo process

The diazo process is a chemical method used in photography and copying. It relies on the light-induced decomposition of organic diazonium salts. These salts, characterized by the N₂⁺ group, are unstable and readily react when exposed to light, particularly ultraviolet rays.123

In diazo processes, these salts are typically impregnated into papers or transparent supports. When exposed to an original image, the light decomposes the diazonium salts in the exposed areas. The remaining, undecomposed diazonium salts can then react with other compounds to form dyes, creating a positive image from a positive original. This process is often used for office copying and microfilming due to its efficiency with flat copy reproduction.1