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576 History of Three-Color Photography
The Omnicolore Plate. — This was the invention of du Hauron and Bercegol (see p. 492), and was introduced commercially3 in 1907, and was made by a resist process.
E. Valenta4 stated that the screen consisted of blue lines from 0.04 to 0.045 mm. width, with green and red rectangles of 0.06x0.07 and 0.05x0.06 mm. respectively, and as a whole the plate had a reddish or bluish tinge. By treatment with hot water some of the red dye was extracted and this had a yellowish-red fluorescence. Acetone dissolved the red and yellow dyes, and microscopically examined, the plate was seen to consist of a broad, bright blue line, and another narrow, dark blue one, and colorless spaces in the place of the red elements. The green was formed thus of a yellow and blue, and the red of a crimson and yellow. Soda lye destroyed the blue dye of the green fields, and the dark blue lines turned violetbrown. The dye of the dark blue lines was destroyed by ammonia, but was regenerated by acetic acid, while the blue dye of the green lines was not attacked. By treatment with hot alcohol the red and yellow dyes were removed, and there remained a system of parallel blue lines. The alcoholic solution was red and fluoresced yellowish-green ; the red dye was precipitated by lead salts, pointing to the use of a fluorescein dye, which would not be conducive to light-stability. And it was found that the red and yellow dyes altered in sunlight, and the whole plate became more bluish.
The red elements were transparent from wave-length 5900 to the extreme red ; the green transmitted from 4800 to 5900, and the blue from 4800 to the ultra-violet. The transmissions were sharper than with the Autochrome plate, and the compensating filter was lighter, yet the plate required three times the exposure of the Autochrome, due to the low sensitiveness of the emulsion. The color-sensitivity extended from B^C to b2/3F, with a distinct minimum at 4500 to 5000, and there were two maxima, so that probably an isocyanin was used. Du Hauron and Bercegol5 gave some general data as to these plates, and stated that there were in every square millimeter about 72 orange-red units, 72 blue-violet, 72 green and 72 purple-violet units. The colors differed sensibly from those used in the Autochrome, the green being less yellow and the blue less violet.
The Dufay Plate. — The first plate, made according to the Dufay patents, was known as the "Diopticolor," and in that the screen was issued for separate use with panchromatic plates. Later the name "Dioptichrome" was adopted, and this plate was issued either coated with emulsion or for separate use6 in which four colored elements were used. The principle of the screen was stated to be7 the creation of a first group of two simple or primary colors, not complementary, which might be red and blue, or red and yellow, or yellow and blue. The superposition of a second group of colors exactly juxtaposed, the colors of which, unlike the first, should be exactly complementary to each other. One of these should be