122
PHOTOGRAPHIC
EMULSION
TECHNIQUE
In 1905, K. Schinzel, then a clerk but seventeen years old, coated a plate with three layers of emulsion, each layer being sensitized for one of the three primary colors, but dyed with the color complementary to it. Thus the red-sensitive layer would be dyed cyan, the green-sensitive layer magenta, and the blue-violet-sensitive layer yellow. It was Schinzel's idea, after developing and fixing the exposed monopack, to treat it with. a weak solution of hydrogen peroxide. The dyes to be used were such that through the catalyzing action of the reduced silver they would be decolorized to an extent proportional to the different densities. Color formers instead of actual dyes were shortly afterwards suggested by thi inventor." The first Mannes and Godowsky patent 10 described an upper self-screened emulsion layer an top of a rapid red-sensitive emulsion. This twO-COIOl路 monopack was developed and fixed in the usual way, the reduced images being afterwards converted into silver ferrocyanide, one for use as a mordant for a basic orange dye; this was done by means of a solution the diffusion of which could be controlled, The other (ferrocyanide) image was then toned with a blue-green toning bath. From this brief description, the beginning of the modern monopack can be appreciated. A three-layer process was meantime worked out by Dr. Bela Gaspar, whose prolific patents date from about 1930. Using black-and-white separation negatives obtained with a split-beam camera, and making from them separation positives, he employed for motion-picture printing in color, nitrate film stock which was coated on one side with a blue-dyed emulsion and on the other side with first a yellow-dyed, and then a magentadyed emulsion. The dyes were destroyed on development in proportion to the presence of developed silver; the image was then bleached and the residual silver bromide converted into chloride, on which the sound track was developed. The whole film was then fixed in hypo and all remaining traces of silver
COLOR-SENSITIVE
123
EMULSIONS
removed, leaving a dye image of great brilliance. Such film was of course applicable to printing only. In a subsequent process," a monopack for exposure in the camera is described. A blue-sensitive layer is coated on the support first, and this receives the lens image. On top of this are coated the green and red layers. A distinguishing feature is that, to speed up the material, dye generators, rather than actual dyestuffs, are used. The blue-violet emulsion, it is suggested, may contain about fourteen grams each of gelatin and silver halide per square meter; the yellow (complementary) dye generator being 0.85 gram per square meter of r-phenyl-jmethyl-pyrazolone-g. The green emulsion layer is colorsensitized with 2-methyl-I-ethyl-pseudocyanin iodide, and contains a dye developer of one gram per square meter of 1amino-Senaphthol-j : 6-disulphonic acid, which is rendered inoluble through precipitation within the emulsion by triphenylguanidin acetate. This layer is made self-filtering by the addition of 0.75 grain per square meter of tartrazin. The top layer is color-sensitized with pinacyanol, using one gram per square meter of diphenylguanidin acetate, and colored by a suitable red dye. The film is developed, fixed, and washed, and the dyes in the two lower layers generated by treatment with a nearly neutral solution of: Water 100 10 Sodium acetate Diazosulphanilic acid 0路5 This is used at a temperature of between 3
0
cc g g and 8 C. 0
The film, after being washed and dried, is treated with a blue dye solution, the dye being precipitated in the top layer. The dyes are then destroyed in proportion to the silver deposits of the images by treatment with an acid solution of thiocarbamide. In the Kodachrome process, after straight development of the three primary images, the reduced silver is dissolved out and