Diazo process is a method of producing copies of documents. A document on opaque paper, translucent paper, or transparent film is placed on a chemically treated sheet of paper and fed into a diazo process reproduction machine. Ultraviolet light shines through the original copy and changes the chemicals on the paper to a colorless compound. But the ultraviolet light does not shine through the dark lines or letters on the original copy. The machine then develops the treated paper by exposing it to ammonia vapor, and the parts not struck by ultraviolet light appear, making a copy.
The diazo process has been largely replaced by other copying methods (see Copying machine ). The diazo process is sometimes referred to as the Ozalid process, named for the Ozalid Company of the United Kingdom, an early manufacturer of diazo process reproduction machines.
