Method of using diazotype photographic materials with preexposure treatment to form uniform sites of refractive index change

摘要

An improved diazotype photoprinting material of high printing speed and its method of preparation are disclosed. The improvement is achieved by distributing through the film coating a substantially uniform distribution of sites having a refractive index substantially different from that of the remainder of the coating. The sites consist of either voids or finely divided solids. Voids are created by contacting the film coating with an aqueous fluid at elevated temperature or an organic solvent for a sufficient period of time to cause a measurable haze to appear on the film. The sites operate to reflect or refract incident light rays during imagewise exposure, and thus increase the optical path length through a given thickness of film.