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494 History of Three-Color Photography
with cinnabar scarlet (von Beyer & Kegel). This penetrated the gelatin and was fixed with ferric chloride. The resist was removed, fresh lines impressed at an angle to the former and methyl blue for silk (Hoechst) was then used and mordanted with ferric chloride. The greasy ink was removed and the uncovered parts treated with a mixture of patent blue A (Hoechst) and yellow F, this being also fixed with the iron salt. The result was six or seven red lines to the millimeter with green and blue units arranged at 45 degrees in between as rhomboids. The colors transmitted by the filters were, for the red down to 5600 ; the green from 5700 to 4800 and the blue from 4900 to the ultra-violet. The various stages are shown in Fig. 132.
C. Spath93 used rubber as a resist for the two sides of celluloid and a series of lines were ruled on one side so as to expose the celluloid and a 2 per cent solution of Victoria blue in absolute alcohol was used. The protective layer was again ruled at right angles to the first lines and the uncovered base stained up with a mixture of auramin and ethyl green in 80 per cent alcohol. The resist was then removed, the uncolored parts were stained up with rubin and auramin in 60 per cent alcohol. In a subsequent patent94 Spath proposed to soften the surface of celluloid so that it would receive a colloid. Acetone and alcohol were used in varying ratios and the base stained up in quinolin yellow, then mordanted with tannin. Greasy resists could be used but the essence of the patent is the use of basic dyes, which are absorbed by celluloid.
L. Dufay95 exposed a dichromated colloid under a matrix line screen, or other patterns could be used. After washing the soluble parts were stained and then a greasy resist applied, which only adhered to the exposed parts. Pulls were then made on to a gelatin coated surface and the dyes were transferred. Before complete drying of the resist the plate was coated with an alcoholic varnish, and as soon as this was dry the resist was removed, leaving the dyed elements covered with varnish. Then another transfer was made from another plate as before and the plate would thus bear two colored elements. The uncolored places were dyed up by contact with a gelatin pad saturated with color.
In a subsequent patent96 the method of applying the resist by means of a spray or copper plate was disclosed. Fig. 133 shows the various stages : 1 and 2 show the first stage in end view and plan, that is the application of the resists c with the interstices d, and 3 represents the result of the dyeing. 4 the layer of varnish, whilst 5 and 6 show the removal of the varnish. 7 shows half the surface covered with resist, 8 the result of the second dyeing and 9 the finished plate. The colors are indicated by the letters, w for violet, 0 for orange and v for green ; 10 to 15 show various patterns that could be produced.
Another patent97 was taken out by Dufay; a resist was applied and lines cut there through to varying depths and stained in various colors;