The history of three-color photography (1925)

478 History of Three-Color Photography screen x was provided with plane surfaces gf flanked by prismatic surfaces r and bs the green rays being incident perpendicularly on the plane surfaces, whilst the red and blue were refracted. In order to render the rays parallel, the condenser w might be used and y to converge the light passing through the linear transparency i. Other suggested forms of prismatic surfaces are shown in 2, 3, 4. M. Petzold8 patented a process in which cold saturated solutions of azo or acid dyes were made in 1 per cent solution of an alkaline chromate, and lines ruled therewith on gelatinized glass; the red and green lines thus produced were dried and the plate bathed in a concentrated solution of rosanilin blue, which only dyed the interspaces. For the red, Bordeaux, orange scarlet or ponceau were used and acid green for the green. L. Horst9 patented a system of forming an image on a line screen and then reducing the two on to a film. , f & y K ~~ — Ilfei w 'J V ifig p. Fig. 125. Ives' U.S.P. 648,784 (Page 476). Dusting-on Methods. — The production of irregular mosaics by the dusting-on of particles seems to have found considerable favor with inventors, though the Autochrome and Agfa plates are the only ones that survive. J. W. McDonough10 was the first to patent this method. He proposed to coat the plates with varnish or like material, that would dry tacky, then dust over the plate a mixture of colors composed of fine or powdery particles, containing the desired colors. Powdered glass, transparent pigments, gelatin, resin or shellac, stained with anilin dyes were suggested; and in the case of glass the particles might be afterwards fused into the body of the support. The preparation with shellac is rather fully dealt with; it was proposed to dissolve the same in alcohol, white shellac being used, and anilin colors were added. The red, formed of yellow and red, was to cut off as much green as possible, in fact to be a pure red. The