Viewgraphs, ContinuedDiazoMaking a viewgraph with the diazo process involves using specially treatedfilms and papers and a diazo printer. Diazo film, foils, and paper treatedwith a mixture of diazo salts and azo dyestuff form images in colors andblack. The salts are light sensitive. After you expose a foil to a light source,particularly an ultraviolet light, develop it in an alkaline medium, such as thevapors of commercial ammonia (ammonia hydroxide) with a reading of 26°Baumè. The salts combine with the azo dyestuff during the developmentprocess to leave an image. Exposure time in the printer is critical, developonly long enough to obtain maximum color saturation.Figure 2-22 shows the diazo process simplified.Figure 2-22. —The diazo process simplified.Continued on next page2-39
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