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488 History of Three-Color Photography
A month earlier, R. E. Liesegang67 had also applied for a patent, and stated68 that screens in which black lines gradually merged into white or one color into another could also be made by this process (Witt's). With such black and white screens it would be possible to obtain half-tone negatives in the camera, without any separation between the screen and sensitive surface. Further it would be possible to print on copper with the interposition of a screen. Dot-form screens could also be made by cutting blocks made as above at right angles to the direction of the lines. Instead of sheets, solution of celluloid or the like might be cast, allowed to dry and the next coating poured. It will thus be seen that there is a clear description of processes subsequently patented.
R. Krayn69 patented this process and suggested the use of a bottom sheet of colorless celluloid as support. In a subsequent patent70 each sheet was to be cast separately, then cemented into blocks. By making cylindrical blocks71 and cutting thin veneers long lengths of film were obtainable. Mosaic screens were also to be made72 by first cutting veneers and then superimposing them into a block and again cutting. There is also claimed in this patent the addition of zinc white to the colored celluloid, so that the film could be used for positive work.
W. C. Masser and W. Hudson73 proposed to cut film into thin threads or bands and apply the latter to another film. The threads might be parallel or crossed, some colorless or opaque. Various modifications were disclosed and a number of films might be clamped to form a disk on a spindle and rotated against a knife, applied at the circumference of the disk. The Vereinigte Kunstseidefabriken74 proposed to make color sheets from 0.125 to 0.15 mm. thickness, and whilst they were in a soft condition to press into a block and cut the same. F. Fritz75 thought the above methods troublesome and proposed the use of materials woven of artificial threads, then combining these into a block and subsequent cutting. The same effect was also76 to be obtained by spinning threads into strands and proceeding as before. Dot or mosaic screens could be made from artificial silk, twisted into a strand.
C. L. A. Brasseur77 also patented the making of cut screens by cutting veneers, as shown in Fig. 126, in which 1 shows the three sheets united, and 2 the same in end and side views, and 3 a block made by superposition of many sheets. The width of the line was to be 1 /520th of an inch, and the thickness not more than 1/2500, and with some colors even 1/4000 of an inch. It was proposed to grind down the sheets, as shown in 4, as it was impossible to cut such thin veneers. The formation of a long screen is shown in 5. F. A. Fifield78 would adopt the same method precisely. Fig. 127 shows the various forms of the finished screens.
M. Obergassner79 would make line or mosaic screens by coating a glass plate with gelatin solution, colored with the requisite color, and cutting lines in the same with a plane, then again coating, again ruling lines and