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