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i yo HISTORY OF COLOR PHOTOGRAPHY
from a solution which is non-penetrating. This is accomplished by dispersing or dissolving the dye in castor oil, castor-oil-alcohol, or gum arabic mixtures.
To insure that the sound-track areas of motion picture film would be left free of screen pattern, C. Bonamico (U.S.P. 2008239; Eng. P. 356816 and 414761), and T. T. Baker (Eng. P. 335899) so constructed the rollers which printed the resists that no deposits were made in those areas which, after slitting, would correspond to the sound-track region.
The next problem to be tackled was that of coating. Here it was necessary to insure the firm adhesion of a gelatin layer to another of rather complex structure, and one which contained basic dyes. These were not always neutral with regard to their action upon the photographic emulsion. Some of the dyes may act as sensitizers, while others may have the opposite action and act as desensitizers. So the simplest procedure to adopt was to insulate the screen layer from the emulsion. This was disclosed by T. T. Baker (Eng. P. 401719; U.S.P. 1962679) and by H. D. Murray, H. Baines, and R. A. S. Grist (Eng. P. 435484). A solution of resin in benzol to which some linseed oil had been added, was the Baker solution.
A complete specification for the formation of the screen is disclosed by T. T. Baker (Eng. P. 420824; U.S.P. 2030163). The reason for this patent is to protect the printing of the resist lines by means of a special roller, where nonprinting areas contain an ink-resisting mercury-silver amalgam. The film base is prepared in the manner disclosed by H. J. Hands (Eng. P. 243032, 281803, 287635, and 301439). On this is coated a thin layer of collodion which is dyed green by the addition of 2 cc of a stock dye to 30 cc of collodion. The dye is prepared by dissolving 4 parts of malachite green and 6.7 parts of auramine in 100 parts of methyl alcohol. A strip 100 by 26 centimeters requires from 22 to 25 cc of the dyed collodion solution. This had been disclosed previously by C. Bonamico and H. Wade (Eng. P. 321222). Upon the dyed film is then printed a series of resist areas, which may or may not be in the form of a geometric pattern, by means of a special roller.
This is prepared in the following manner. A metal roller is first given a coating of silver. Upon this is deposited an even coating of chromium, also electrolytically. On top of the chromium is placed a sensitized tissue upon which the screen pattern has been photographically printed. The tissue used is a dichromated gelatin or other colloid. It is placed with the image portion adjacent to the surface of the roller. Treatment with hot water removes the non-image portions, leaving a tanned colloid relief image upon the surface of the roller. This is next subjected to the action of a solution which will etch the chromium wherever this surface has been laid bare, obviously between the tanned colloid relief areas. When the chromium surface has been etched away, leaving bare the silver, the etch is stopped. The tanned colloid resist is removed, and the roller treated with a mercury solution. Only the silver will form an amalgam, the chromium being insoluble in mercury. An amalgam surface has the extremely useful property of acting as a resist to greasy inks,