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Printing from Screen Plates 561
paper so as to show complementary colors, and then the exposure made. Registration was rendered easy by using non-expansive translucent paper and by pins in the printing frame. It was also suggested to use deeper colored screens for transparency work and bleach the image with mercuric chloride.
G. S. Whitfield86 patented the production of separate color constituent positives from screen mosaics by means of a masking key screen, which had a pattern in black or color to mask two of the color records of the screen negative. The taking screen had registering bands at the ends of the plate and superposed on the pattern-taking screen, which stopped one of the colors and transmitted the other two. The key-masking screen had at the ends a color pattern area the same as the pattern of the taking screen. This masking screen was registered correctly with the screen negative so that only a single color was seen. A. C. Eastman,87 C. L. A. Brasseur88 and Whitfield89 also patented registering marks.
E. BoubnofP0 patented the production of photomechanical prints by the use of negatives through linear screens, making a positive in relief, fixing the latter on a cylinder and using the relief as the control of a spray apparatus that applied color to paper. S. SchapavolofP1 would dye the screen elements twice in the same color, one application being fixed and the other subsequently removable, thus utilizing the same idea as Ruth and Schuller (see p. 553), and Krayn (see p. 555). L Dufay92 proposed to use a double-coated film, panchromatized and impregnated with a lightrestraining dye, so as to prevent the light from penetrating from one side to the other, and then to print from a complementary colored negative, using selective filters. The third image might be obtained by any other process, such as imbibition. The same inventor5'3 would print from screenplates in the complementary colors. Prints were to be made on panchromatized film or bromide paper through selective filters and the images converted into red, yellow and blue for superposition. Or the images might be tanned with acidified solution of dichromate and bromide of potassium. When bleached, the print was inked up with its appropriate color, after being etched with glycerol and water, as in collotype. The images might be transferred to stone, zinc or copper and further treated for lithography, half-tone and photogravure.
MM. Lumiere & JouglatM patented method of impregnation of a bleach-out paper, before exposure, with solutions of hypochlorites, hypobromites or hypoiodites with addition of chlorides, bromides or iodides of the alkaline or alkaline-earth metals. Thus a paper might be prepared with a mixture of erythrosin. anthracen and methylen blue, and be subsequently immersed in a solution of eau de Javelle. Among the hypochlorite compounds suitable for the process, were those of sodium, potassium, barium, strontium, magnesium, aluminum or zinc. The concentration was so chosen that in using sodium hypochlorite about 25 to 30 per cent of
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