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Double-Coated Stock 641
might then be dried, one side protected by a waterproof varnish and the other side converted into a complementary green by treatment with a ferric salt. Or the second solution might be applied to the wet film by suitable rolling or brushing devices. W. F. Fox, W. H. Hickey and Kinemacolor Co.11 also claimed the use of double-coated stock, but one of the pictures was in black and white, and the other side in colors only. Later Fox12 proposed to use this form of positive stock, and the process is referred to under subtractive processes.
F. E. Ives13 also adopted the use of it with copper mordant toning for one side and cyanotype toning for the other. I. Kitsee14 would use dichromated gelatin dyed up prior to exposure and the complementary records were printed on the same through the necessary filters. That is to say, the red record was printed through a green screen and the green through a red. After exposure the soluble gelatin was washed away, the exposed parts retaining the color.
W. V. D. Kelley15 also patented the use of double-coated positive stock, suggesting a spray for applying solutions and a protecting coat of celluloid varnish to one side while the other was being treated with dye solution. In a subsequent patent16 the use of this stock with a four-color record negative was also claimed. Kelley also patented an additive process.17 Double-coated stock was used and exposed through a screen of symmetrical pattern, such as lines, dots, etc. The screens for each side being displaced so that the exposed parts of the one side were opposite the unexposed parts of the other. The two-color negatives were then printed on opposite sides in registry and the film further treated as usual. The result being that on one side there were all the blue-green images, broken up into geometrical spaces of clear gelatin, and on the other side all the red images broken up in like manner. But the clear spaces on one side not being superimposed on those of the other, but juxtaposed, they all acted like small windows through which the images could be respectively seen, no matter from which side the picture was examined. The result optically was a two-color screen-plate positive with the color units on opposite sides of the support.
P. D. Brewster18 would apply the double-coating principle to negative stock, and proposed to insert a stained medium between one emulsion layer and the base to prevent the colored light from penetrating through the support to the other side. One side was sensitized so that it would record one group of colors, for instance blue and green, and the other so that it would record the red and orange. After completion, the image on the front of the film, that nearest the lens, was to be toned blue-green and that on the back red or orange. From this colored negative, a positive was made on double-coated film, one side being coated with a perfectly transparent emulsion stained yellow, sensitive to blue and green, while the other side was sensitive to red. Modifications were suggested, such as
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