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CHAPTER XVIII SCREEN-PLATE PATENTS
Linear Screen-Plates. — The honor of making the first line screen, as outlined by du Hauron, may be fairly divided between J. Joly and J. W. McDonough. The former1 (page 507) suggested the use of the color sensation curves (see p. 457). He also ruled plates with diagonal or other lines forming a filter screen that was placed in front of and in contact with a color-sensitive plate. Various pigments or dyes could be used, chrysoidin orange for the red; a mixture of ethyl green and chrysoidin for the green and water blue for the blue-violet. From the negative obtained in the camera, an ordinary black and white positive was made and bound up with a viewing screen, ruled in like manner but not with the same colors. In this case the colors were like the lithium line in the red, a green like the E line and a lapiz-lazuli blue. The lines should be 200 to the inch, and it was suggested that the same screen could be used for taking and viewing and then the emulsion might be coated on the top of the lines.
McDonough2 also patented the same idea and disclosed the use of glass, mica or celluloid as the support, and various patterns of lines and mosaics, as shown in Fig. 122, in which the letters R, G, B stand respectively for red, green and blue-violet, and he proposed to provide the plate with registering patterns, marked T and 0. Later he proposed to use various patterns, and also more than three colors, as shown in the letters R, 0, Y, G, B, I, Fig. 123, which obviously mean the seven colors of the spectrum.
Macfarlane Anderson3 proposed to use a frame carrying a number of parallel wires with interspaces half the diameter of the wires, the color filters were placed in front of the lens, and after an exposure with one filter, it was changed and the wire frame shifted so as to cover the exposed part and this operation repeated with each color filter. This method was primarily intended for photomechanical work. F. J. Harrison4 proposed to use a "color ribbon," that is a length of celluloid uniformly stained and ruled with opaque lines, Fig. 124, in staggered pattern, twice the width of the interspaces. This was moved by clockwork in front of the sensitive surface in parallel with the lines and the result would be as though the lines had been ruled in juxtaposition on one surface.
C. L. A. Brasseur and S. P. Sampolo5 patented the use of a black and white screen in front of a tri-color linear screen, the black lines being twice the width of the interspaces, and this screen was shifted between the exposures. F. Faupel6 patented a process for obtaining linear and other patterned plates by coating a surface with a colloid and then ruling with a
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