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History of Three-Color Photography
Brewster47 would use a long, narrow tank, Fig. 184, in which the film 2 runs face down over the liquid, being moved by the sprocketed wheels 21, 22, and kept under a slight vacuum by means of the suction pipe shown above. Two tanks were used, each containing one of the dyes, and between them was placed a wash tank containing constantly renewed water, in which the film took a 180° turn, so that in the second tank the other face was presented to the other dye, which was either to be sprayed on or thrown by means of the revolving brushes, driven by a common drive.
J. G. CapstafT48 used a long, narrow trough, provided with a plurality of parallel capillary rollers, which revolved in the dye and carried enough to stain up the positive image as the film passed over them ; tension rolls between the dyeing rollers regulating the contact surface of the film with the dyeing rollers. An exhaustion box was also fitted which removed excess of dye from the surface of the film. The machine is shown in Fig. 185, and the film runs from right to left. It is unnecessary to enter more
Fig. 185. Capstaff's U.S.P. 1,351,834.
fully into the constructional details, as the operation is sufficiently clear from the diagram.
J. Mason49 conceived the ingenious idea of treating one side of the film by floating it on the surface of a solution, thus taking advantage of the surface tension. It is obvious that this method does away with any inflatable drums or spraying methods and is extremely simple and effective in action. Besides that the necessary troughs being very long and narrow, in fact they need be but little more than the width of the film itself, space is much economized. J. I. Crabtree50 patented the use of an inflatable drum, covered with rubber and behind which air or other fluid could be pumped after winding on of the film. This was practically the arrangement used by the author in 1911.
J. H. Christensen"1 patented a process in which the supports were stretched in a frame prior to exposure, thus preventing any contraction and expansion in the subsequent baths. A. Hamburger52 described a