Question

explain the role of ammonia solution, diazonium salt and halogen lamp in developing of the colorful image formed in dye coupling and diazo imaging

Answer 1

These contain diazonium salts in the coating layer that combine with dye couplers to produce strong, dense colors. Exposure to UV radiation causes the salts to decay and to lose this coupling capacity. In the diazo process, film is exposed by contact printing from a master. Acids used in the coating to prevent the coupling reaction are neutralized by exposure to a strong alkali (usually ammonia), and dyes form in unexposed areas of the film. The image duplicates the master directly. Diazo film is available in a variety of colors, including black. It may have an acetate or polyester base, although polyester is increasingly popular because of its stability and resistance to environmental factors. Resistance to fading depends on the choice of salt and dye coupler; black requires a combination of dyes. Processed black diazo resembles silver gelatin film but is glossy on both sides. Diazo film is reasonably stable but eventually fades, even in the dark. Fading is accelerated by prolonged exposure to light.