The history of three-color photography (1925)

502 History of Three-Color Photography tion of blacks. This is essentially the principle used in the Dufay patent (see p. 494). C. Spath146 proposed to make ruling machines for fine line work by alternating on a steel rod, pieces of triangular steel 0.05 mm. thick and 18 mm. wide, with celluloid triangles of the same dimensions. These were tightly clamped together, the edges brought into coincidence and the celluloid partly dissolved, leaving the steel as sharp ruling pens or planes. J. H. Powrie147 patented a method of obtaining fine line screens without overlapping of the edges. A matrix screen with registering bands on two opposite edges was used. These registering marks were opaque and transparent lines, and an opaque and transparent band were termed the margin interval. It is claimed that this method permits of ocular registration without the use of a microscope. W. C. Huebner and C. Bleistein patented148 various cameras, in which screen patterns were formed immediately in front of the sensitive surfaces by altering the shapes of apertures ruled in compound screens of black and white. A. W. Carpenter149 patented the use of a pulverisable material, such as soft paraffin wax, reducing this after dyeing to an impalpable powder by liquefying and atomizing synchronously into a congealing chamber. The spherical particles thus produced were to be compressed into blocks and cut by means of a microtome into thin laminae and these transferred to a suitable support. The Naturfarben-Film G.m.b.H150 proposed to coat a transparent support with a thin silver emulsion, expose under a matrix screen and develop right through to the support. Then treat the image with an agent that would harden the gelatin in situ with the silver and bleach or dissolve the latter, then wash out the unhardened parts with hot water and dye up the hardened parts. H. Butschowitz151 patented a method of making the color elements on the emulsion and hardening the same by development, so that the parts removed left the screen. J. H. Christensen152 further patented the emulsifkation of dyed lac solutions in thick rubber solution, or in this plus dammar. The main part of the rubber was removed by washing with benzol, etc. The colored particles were then suspended in a liquid and after mixing in suitable proportions applied to the carrier. K. Frohlich153 proposed to emulsify dyes in a resinous or oily medium and spray on to a gelatin-coated support, 1. E.P. 14,161, 1894; Brit. J. Phot. 1894, 41, 458. 730; 1896, 43, 553, Supp. 39; 1895, 42, 774; 1897, 44, 85; Supp. 84; 1898, 45, 215; Supp. 29; 1899, 46, 264, 380, 774; abst. 1907, 54, Col. Phot. Supp. 1, 16; Photography, 1897, 68; Trans. Dublin Roy. Soc. 6, (2), 127; F.P. 240,933; D.R.P. 94,051; Silbermann, 2, 380; Can.P. 51,125; Nature, 1898, 53, 91; Phot. Times, 1894, 24, 337; 1895, 25, 292; 1897, 27, 531; Phot. Chron. 1895, 12, 115; Phot. Woch. 1895; Jahrbuch, 1895, 9, 213, 512; 1896, 10, 419; Phot. News, 1895, 39, 419, 4S5 ; Phot. Mitt. 1895, 32, 14, 125, 278; 1898, 35, 273, 289; Photogram, 1896, 3, 31; 1899, 6, 205; Process Photogram, 1896, 3, 103. Cf. R. Neuhauss, Phot. Rund. 1895, 9, 380; 1898, 12, 155. when the dyes were absorbed by the gelatin, through the thin skin of the emulsifying agent. A. Hesekiel, D. Phot. Ztg. 1898, 22, 356. J. S. Gibson, Eng. News, 1898, 39, 298;