shown on the lower left and can be compared with a typical diazo film 
coating shown on the right. Gelatin-silver-halide coatings are applied to 
the surfaces of the supporting plastic, Diazo coatings are solvent coated 
and are imbedded into the plastic supporting material. For this reason 
printing exposure made through diazo films are less subject to light 
refraction at coating surfaces. 
FIGURE NUMBER 2 - COMPARISON OF SILVER-HALIDE AND DIAZO FIIM3 
Diazo films have many advantages over gelatin-silver-halide films as 
shewn in Figure 2. Diazo films are exposed to strong actinic light 
sources and are processed to completion in warm moist chemical vapors in 
very short periods of time. They have very high image definition and 
very high dimensional stability and are very insensitive to nuclear 
radiation. Gelatin-silver-halide films require exposure to low intensity 
blue or panchromatic light and require time consuming, messy, three step 
chemical processing followed by drying. Processing time, temperature, 
and agitation must all be carefully controlled. Processing chemicals 
must be constantly replaced or replenished with careful control. Gelatin- 
silver-halide films have somewhat lower image definition than diazo 
films, have relatively lower dimensional stability, are susceptible to 
scratching and abrasions, and are highly sensitive to the fogging effects 
of nuclear radiation before they are developed. 
FIGURE NUMEBR 3 - U.V. AND VISUAL DIFFUSE TRANSMISSION IENSITY 
Black azo dye images are formed by a careful balance of coupling of 
cyan and yellow dyes. This figure shows that the visual diffuse trans 
mission density of a black azo dye image which is a useful measurement 
of the density which a photo interpreter can visualize, does not neces 
sarily represent the reprint characteristics of the black dye image for 
actinic light printing. Any slight imbalance in the formulation of a 
black diazo film can result in a tend to shift the black image toward 
sepia or cyan hue. 
FIGURE NUMBER 4 - IMAGE SPECTRAL ABSORPTION CHARACTERISTICS 
a 
This is recording spectrophotometer trace of a typical black azo dye 
image. The absorption dip at the 39°° Angstrom area allows near U.V. 
light used for printing to slightly lower the reprint contrast while 
maintaining a high visual black dense image. 
FIGURE NUMBER 5 - SENSITOMETRIC CURVE - LOW CONTRAST BLACK DIAZO FIIM 
Positive working diazo film produce direct positive images. They 
require exposure to strong ultraviolet and visual blue light. The light 
penetrating the low density areas of the original film being printed 
destroy the ability of the diazo chemicals to couple an azo dye image. 
Unexposed areas of the diazo film, when subjected to warn moist ammonia 
vapor cause coupling of an azo dye image. Where the original being 
printed is dense, the diazo copy has high density; where the original 
being printed is transparent, the diazo copy has low density. Thus a