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666 History of Three-Color Photography
would be necessary to block out, in each group (this would seem to be the most difficult part of the process, but I think it might be done), and the resulting plate would form one of the color blocks. Four blocks thus made would represent the three colors and a key, which might be printed in black or grey according to taste. This plan only requires one negative, and by correct registering, each dot would be separate from the next, unless strongly lighted, when it might overlap its neighbor at the edges."
W. Giesecke, of Leipzig, took out a German patent22 which while really designated by the inventor as a linear process, is obviously a refraction method, or can be used as such. The specification is worthy of study as the theoretical considerations of the formation of the images is very complete, though marred by erroneous conception of the Joly screen-plate method and the effect of mixing colored lights.
Another patent embodying all the points of Giesecke's was taken out by J. Szczepanik,23 this latter being applied for on April 12, and Giesecke's German patent on May 30, 1899. F. E. Ives also patented the same idea.24 The exposure might be made simultaneously or simply by shifting an opaque line screen. The camera was preferably of fixed focus, and for focusing near objects a supplementary lens was interposed. J. de Lassus Saint-Genies25 apparently ignorant of the work of others also brought forward as novel the use of the three-colored diaphragm.
E. R. Clarke26 patented a three-color process, in which all three colors were first printed on one negative, one or more groups being then printed on separate plates by means of masks photographically made. In the diaphragm of the lens were three apertures, each covered by a filter. In front of the sensitive plate was placed a screen of fine apertures, each of which threw an image of the diaphragm apertures on the plate. The image was thus made up of three groups of dots representing the three primary colors. A mask was then made by placing another plate in the camera, and exposing through one of the apertures. From this negative, a positive was printed and before development, a printing from the tricolor negative superimposed. When developed a positive representing only one color was obtained. Colored films thus obtained might be superimposed. M. Raymond27 also suggested the use of this method, with one large prism of narrow angle, or a series of small prisms, superposed base on apex, the angle of the prisms being from 3 to 8 degrees.
Lenticular Supports. — Although the supposition may be erroneous, still one may be excused from attributing to Lippmann the germ of the following process, in which the support of the emulsion is formed into lenticular shapes. He had proposed28 a film of celluloid or collodion, which before it had thoroughy set, should be impressed with a sort of honeycomb structure, so that it would be covered on both sides with small hemi-spherical forms. The spaces between these tiny lenses were to be filled with a black material, and each lens, of very wide angle, would form