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482 History of Three-Color Photography
so that the celluloid spheres would roll thereon. As soon as the surface was completely covered it was subjected to heat, moisture or spray so that the spheres adhered. The paper was transferred face down to celluloid cast on a flat surface and heat and pressure applied, so that the spheres flattened out, the paper being stripped. If there were interstices, they might be "daubed over" with dichromated gelatin and exposed to light through the back. Black and white screens might also be made by this method. Subsequently27 the same inventor proposed to print on paper coated with an adhesive, with a copper plate, using some liquid that would render the coating adhesive, then applying the grains, again printing with a moistener and repeating for the other two colors. The colors would be thus symmetrically arranged and could be transferred to glass or celluloid.
C. F. Bleecker28 proposed to make spherical granules from glass, silica or borax, especially low-melting colored lead glass, grinding and sifting the particles till all of the same size, then allowing them to fall through a gas jet, burning under a pressure of about 20 pounds per square inch, which fused them into spheres, and blew them into a cooling bin. The particles might be again sifted and dusted on to a support. C. Schleussner29 suggested sifting colloid particles on to surfaces coated with glycerol and glacial acetic acid, evaporating the acid and then applying steam till the particles joined up.
I. Kitsee30 would coat paper with gum solution, dry and coat with celluloid in amyl acetate or other solvents, but not in alcohol-ether, dry and then cut the celluloid by the same machinery as used for half-tone screens, into squares ; it being an easy matter to make cuts every five-hundredths of an inch, and it is possible to go as high as eight hundred, thereby making individual pieces small enough to require more than half a million to the square inch. After the film had been cut, the support was soaked in water, so that the gum was dissolved and the small pieces released. The different colored pieces were then well mixed and applied to their final support. The same inventor31 would dissolve soluble cellulose or gelatin, and spray into a large and high compartment, collect the particles and apply by spray to a tacky support.
M. Wieland32 proposed a phenol-formaldehyde condensation product, a suitable coloring matter being added. An intimate mixture of such globules was dusted on to a prepared plate, excess removed and the plate so heated that the globules softened and coalesced, and the hardening process was completed by pressure and heat. A final coat of colorless condensation product was to be applied.
H. W. H. Palmer33 proposed to use casein or gum, which can be rendered insoluble in water after dyeing, to grind and mix the powders till the first black condition was satisfied and then apply to glass. On standing the grains absorbed moisture and could be flattened out by pressure, thus filling the interstices. Later Palmer34 proposed to use ceramic colors,