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Screen-Plate Patents 481
pensating filter by a colored substratum below his filter elements, gamboge with a little red being specified. He claimed that this did not slow the plate nor interfere with the optical adjustment of the lens. With the latter claim there can be no dispute, but as to the former, it is, of course, immaterial where the filter be interposed, the effect on exposure must be the same. Gelatin, as the color carrier, was later20 abandoned by Bamber and he used sandarac and castor oil, dissolved in alcohol, stained up and allowed to evaporate and powdered. The support was to be coated with a mixture of sandarac, castor oil, oil of lavender and alcohol, and the dry powder dusted thereover ; the castor oil being to prevent the grains cracking. After superfluous grains had been dusted off, the screen was submitted to the vapor of alcohol, wood naphtha, acetone, etc., and the grains already softened by absorption of some of the essential and fixed oils were quickly liquefied by the vapor, and capillary attraction between the grains is said to have drawn the liquid colors into the smallest spaces, leaving the screen gapless and transparent.
H. W. H. Palmer21 proposed to make the color grains by spraying colored solutions into an elongated chamber, and catching the small particles thus formed. The solution might be gelatin, gum arabic, tragacanth or the like, hardened with formaldehyde; or celluloid or colloids; or dammar, mastic, lac or the like might be dissolved in amyl acetate, benzol, alcohol or other spirit and the particles after application to the support might be flattened out. It is also disclosed that liquid colored glass might be blown into fine particles and subsequently fired to make a mosaic. The celluloid or colloids mentioned might be blown on to celluloid film during manufacture, while the latter was still plastic and passed through polished steel rollers, or the colored particles made of materials having no affinity for the components of the liquid celluloid mass, might be incorporated therewith, and so form part of the film in the making.
F. L. Dyer22 proposed to make the colored particles by atomizing a solution of celluloid in amyl acetate, into an electrically polarized atmospheric field, produced by the convective passage through the air of a current of high tension23 and the fibers thus formed were to be subjected to intense cold, such as liquid air, and then powdered. R. Ruth24 also suggested producing the color elements by atomizing gelatin solutions, resins or colloids, and allowing the particles to settle on to a tacky surface ; the height of the atomizing chamber being so adjusted that they would be dry when they settled. In a later patent25 Ruth proposed to add colors to a panchromatic emulsion and atomize the mixture in the same way.
C. L. A. Brasseur26 suggested cutting blocks of celluloid of the desired size, or sheets, threads or filaments of artificial silk, after coloring, and then to roll the small particles between disks or plates till they assumed a spherical form, either with or without heat. A sheet of paper was stretched on a flat board, etc., and coated with a tacky material and allowed to dry,