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498 History of Three-Color Photography
R. J. Cajal112 described a somewhat theoretical method in which colored fibers were imbedded in celloidin and then sections cut with a microtome. The threads were first stained up in anilin dyes, which must not be soluble in 36 deg. alcohol. After staining the fibers were to be left for about 34 hours in syrupy celloidin, with which was incorporated some opaque powder, then withdrawn and compressed into a mass by a circular compressor, and plunged into 36 deg. alcohol for coagulation. The best sections were 0.025 to 0.03 mm. in thickness ; in all cases the thickness had to be adjusted to the colors. The colored particles were homogeneous, cylindrical and produced a uniform effect. The celloidin between the particles stopped the least trace of white light, through the opaque particles, which were metallic silver made by adding silver nitrate with pyrogallol and ammonia to the celloidin. The definition of the image depended upon the regularity and fineness of the sections; when using silk fibers the diameter of the disks did not exceed 5 to 8 microns.
M. Ratignier and H. Pervilhac113 would let colored fibers into celluloid as it was cast. The threads were wound on bobbins and passed through combs, which distributed them on the cylinder, about one-fifth of the circumference from the hopper, which contained the dope. Artificial silk was preferred and after dyeing arranged in sets of three, and the teeth of the combs were so arranged that the fibers touched one another, and became part and parcel of the film. Woven cloth might be used and then mosaic screens would be formed.
F. Fritz114 pointed out that it was well known to use colored fibers for woven fabrics for screens, but that these had the disadvantage that white light passed through the interstices. This he proposed to overcome by using threads of artificial celluloid which could be softened by heat. Fabric was woven in the usual way, then pressed between hot plates, so that the fibers softened and filled up the interstices. In a later patent115 he proposed to imbed a fabric in a plane and plastic layer, which was stained with a color complementary to the warp threads, which were made of cellulose acetate, that is soluble in chloroform, glacial acetic acid and acetylen tetrachloride, but not in alcohol, ether or benzol. The weft threads were nitrocellulose and the imbedding layer gelatin. After drying, the weft was dissolved by alcohol-ether, which did not affect the acetate threads, and the colorless gelatin, not covered by the dyed threads, was dyed up with a dye that did not affect the acetate threads.
A. J. Jorelle116 proposed to use natural or degummed silk, artificial silk or spun glass, either singly or spun into threads and cemented to celluloid with collodion. A. N. Pierman117 also patented the use of spun glass or silk woven into a fabric, using a weft of fibrous character but colorless, the strands being placed so close together that white light would not pass. E. B. Smith118 followed on the lines of Ratignier and Pervilhac and guided threads of celluloid or the like through combs, but in this case the base was