GB560145A - Improvements relating to the production of photo-mechanical printing surfaces - Google Patents

Abstract

560,145. Photo - mechanical printing surfaces. ZIEGER, E. June 25, 1942, No. 8736. [Class 98 (ii)] - A negative of one colour aspect of a design, for use in the production of a printing surface, and having screen markings of varying degrees of fineness to represent various shades of said colour, is prepared by making a series of sketches from the design, the first having opaque areas corresponding to the parts of the design which 'are of one colour though of different shades thereof, and the remainder having areas corresponding in each case to the parts of the design which are of one shade of said colour, the shade chosen differing from sketch to sketch ; photographing the first sketch on to a sensitive plate or film by means of light passed through the transparent parts ; and then photographing the'remaining sketches successively in registered superimposition on the same plate or film, the light from each of said remaining sketches being passed through a screen or shading medium of mesh selected according to the depth of shade required in the corresponding image. The design shown in Fig. 1 comprises parts a, b representing two different shades of one colour, and a part c representing a different colour. The first sketch made is opaque over areas a, b, but transparent elsewhere, and it is photographed by transmitted light on the plate or film. The second sketch is opaque over the area b only, and is photographed in registered superimposition on the.same plate or film using light transmitted through the sketch and a coarse screen. Finally, this sketch is again photographed on the plate or film, this time using light reflected from its opaque areas and passed through a fine screen. There results a negative, shown in Fig. 6, having a coarse screen pattern # in the area a, having a fine screen pattern h in the area b, and opaque in the area c and the area surrounding a. Where more than two shades of the colour are to be taken into account, further sketches are necessary, each being photographed with an appropriate grade of screen or shading medium. When exposures are made using light transmitted by a sketch, the photographing step may be replaced by a contact printing step.