Ozalid process

The ozalid process is a process of printing positive images on paper from patterns on film or other translucent media. It is akin to creating a photogram, using chemically treated paper.

A transparent film with the pattern to be printed is placed on a diazo compound coated paper. This sandwich is exposed to ultraviolet light. After a 15 sec to 5 min exposure, ammonia vapours are used to develop the film image on to the paper.