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560 History of Three-Colo?' Photography
of the subject on to a screen-plate in the dark room and then photographed this compound image. F. S. Soudet7-' proposed to make three separation positives and project in superposition.
The Socicte Anonyme la Photographie des Couleurs73 patented the fusion of the colors by treating the support with a solvent for the vehicle. The same inventors74 proposed to suppress the compensating filter by shading the different color elements with a neutral color. This plan was first suggested by du Hauron (see p. 455). Later they also would use75 elements on paper complementary to those of the negative screen-plate. H. Hudson76 would use non-reversed screen negatives and print in three successive dichromated-gum films, using color filters.
H. Pedersen77 would make a mosaic screen on a transparent support with the elements dyed with colors soluble in alcohol, but insoluble in water. This was then coated with emulsion, containing a white pigment. After the usual operations the plate was treated with a bromoil or other hardening solution, fixed and developed with hot water and dried. Then a sheet of gelatin, impregnated with alcohol could be applied and the colors would diffuse through the variable thickness of the image into the gelatin, which was then stripped and applied to a black support. Precisely the same patent was granted to O. Fielitz.78 M. Poulot79 would use a mixture of gelatin, ferric chloride and tartaric acid coated on one side of a transparent paper, the other side being coated with a dichromated screen. G. Jousset80 proposed to obtain negative and positive and paint with colors and then reproduce with a screen-plate.
L. Heck81 would expose a panchromatic plate in contact with a screenplate, then make three positives on glass and expose on dichromated fish glue and strip and transfer to paper. M. H. Poinsot82 provided paper with red, yellow and blue elements, sensitized and exposed and then immersed in a bleaching bath, which acted through the insolubilized parts. The paper might be fixed to glass or metal for registration and a greasy line resist used to protect the colors. A Bueno83 made three negatives from a screen-plate and from these reliefs. Three styluses were electrically moved over the reliefs, on the system of the pantograph, and traced the images on prepared paper.
K. Warga84 proposed to obtain an ordinary black and white positive from a negative, taken without a filter, and stain the same yellow. And from the blue-filter and red-filter negatives, taken at the same time as the other, print-plates were made on dichromated gelatin, coated on a metal band, and the images inked up with greasy inks. They were then immersed in dye solutions and the dye images transferred to a yellow-stained positive. L. Dufay85 proposed to use a regular geometrical screen for taking and a similar patterned screen on papor, with much fainter colors, coated with a positive emulsion. After a negative had been made on a panchromatic plate by the separate method, it was applied to the positive