The history of three-color photography (1925)

452 History of Three-Color Photography for the blue. These should be preferably made up in 1 per cent stock solutions and about 3 per cent acetic acid added, except for the red dye, which is decomposed. The prints or transparencies should be immersed for some time, being examined about every half hour. When sufficiently intense they should be rinsed in water, acidulated with acetic acid, till the high lights are colorless. R. Fuelgen28 would obtain accurate registration for additive projection, by providing the plate holders with a special rebate so that the plates occupied a definite position as regards the camera, and the printing frame and lantern slide carrier were also provided with a similar rebate. S. Procoudin-Gorsky29 patented a frame by means of which the three constituent positives might be printed in register. P. D. Brewster30 patented the use of a mixture of potassium carbonate, glycerol and formaldehyde for the stripping of the constituent images from glass plates, and the use of caustic soda and formaldehyde, followed by an acid with glycerol, for stripping films for transparencies. H. Diernhofer31 also patented a frame for holding three-color component transparencies for simultaneous projection. The middle one was fixed and the outer ones adjustable, so as to secure registration. Farbenfabriken vorm. Bayer32 patented the use of a film, coated with a lightsensitive emulsion, the back of the film carrying a film of gelatin capable of absorbing dyes or pigments. This was for transparency or reproduction purposes generally. E. F. Griin33 stated that the ordinary lantern plate, opal or bromide print might be used for the primary image and after fixing and washing the image converted into a cyanotype blue and the gelatin sensitized with dichromate for the red and yellow impressions. A. Nefgen34 proposed to make a transparency of an original and paint with the three fundamental colors and from this make negatives with suitable filters. H. A. Rogers35 proposed to combine the parallax system with color results by using a colored screen in conjunction with colored, black and white or neutral tinted pictures. The lines of the screen might be opaque, translucent or transparent. The lines forming the picture might be consecutively in different colors, red, yellow and blue, or each line might itself comprise more than one color. Or the picture might be printed by an ordinary three-color process. 1. Bull. Soc. franc. Phot. 1867, 14, 124; Handbuch, 1917, 4, II, 187. 2. J. Camera Club. 1891, 6, 135; Phot. Nachr. 1891, 3, 582; Jahrbuch, 1892, 6, 454. In Bull. Soc. franc. Phot. 1898, 45, 265, 306, L. Vidal used roll films (Eastman) coated with emulsion, sensitized with 2 per cent ammonium dichromate and used for dyes, erythrosin, ammonium picrate and methylen blue. In Bull. Photo-Club, 1898, 724 he suggested methyl green for the blue, erythrosin plus eosin yellow for the red. E. Dunmore, Brit. J. Phot. 1894, 41, 504 also suggested the use of stained gelatin films superposed. "G. L." Phot. Coul. 1906, 1, 23 also used roll films. 3. St. Louis Phot. 1895; Tahrbuch, 1895, 9, 418; Handbuch, 1917, 4, II, 207. 4. Jahrbuch, 1896, 10, 160; Bull. Soc. frang. Phot. 1898, 45, 316. 5. D.R.P. 101,132, 1895; Silbermann, 2, 369; Phot. Rund. 1895, 9, 217; E.P. 7,104, 1895; Brit. J. Phot. 1896, 43, 39, 78; Jahrbuch, 1896, 10, 240.