GB478319A - Improvements in color printing processes - Google Patents

Abstract

478,319. Photo - mechanical colourprinting surfaces. HAPKE, A. G. July 14, 1936, No. 19564. [Class 98 (ii)] In preparing blocks for colour printing, a set of positive prints is taken from the original negative on a waterproof plate having a smooth white surface and sensitized to produce a blue-print positive, the parts which are to appear in the final result in one colour are blacked out, the residual image is removed, and the plates are photographed through screens to produce a set of negatives from which the blocks are made. A different screen ruling is used for each block. White areas in the final print are produced by blacking only the outline of the area on each plate. Fig. 1 shows the original plate with the blue areas blackened, Fig. 4, the same plate after the removal of the unwanted parts, and Fig. 7, the resulting screened negative. The plates used may be of white enamelled metal and sensitized with a standard blueprint formula, e.g. ferric ammonium citrate and potassium ferricyanide with the addition of gelatin and albumen and after exposure are developed with a solution of alum and potassium bichromate. The blackening of the areas to be preserved is performed by hand using a chart of shades of grey to guide the colour reproduction.