Diazo Copying

(also called diazo process photocopying), one of the most widely used methods of reproducing technical documents on the basis of the diazo process. Diazo copying is an economical, convenient method of reproducing technical documents, blueprints, graphs, and textual materials of any format.

In diazo copying the photocopies are made on special photosensitive papers (such as SSN-2, SK-5, and MP types) that have high resolution, contrast, and coloring (various gradations of black and brown). Upon exposure the latent image of the original is formed on the diazo paper: the diazo compound is decomposed, remaining only in places on which the light was not incident, that is, in places that correspond to the elements of the image. To bring out the copy, the diazo paper with the latent image is developed in an alkaline medium (ammonium vapors in the “dry” method; an alkaline solution in the “wet” method).

Diazo copying can be done from any original. For this purpose it is necessary first to make a copy on a translucent base (tracing paper, phototracing paper, reflex paper, transparent paper, or transparent plastics). Duplicates of the original are often made on diazo tracing paper with a cellulose or cotton base. Diazo copying is most often done by the contact method on photocopiers designed for simultaneous exposure (formation of the latent image) and development of the copy. The photocopiers are equipped with powerful controlled light sources (usually mercury lamps) and an electric drive with smooth control of the rate of feed of the photosensitive material. This makes possible the production of copies with diazo materials of varying photosensitivity from extremely diverse originals. Special devices that can be incorporated into a photocopier are made to mechanize the trimming of photocopies when working with roll diazo papers. Projection diazo copying, which makes it possible to print magnified copies from microphotocopies (microfilms) on diazo papers, is becoming increasingly widely used.

a copying process based on a property of diazo compounds, by which the compounds lose a color-forming substance under the action of light (ultraviolet rays). The copies (diazotypes) are prepared in automatic and semiautomatic machines on paper, tracing paper, or film covered with an aqueous solution of a diazo compound. Diazo copying is simple, economical, reliable, and convenient, since the process does not require darkroom conditions.