GB571107A - Improvements in photographic stencils - Google Patents

Abstract

571,107. Photographic wash-out reliefs; photo - mechanical printing surfaces. KODAK, Ltd., and STEVENS, G. W. W. Jan. 31, 1944, No. 1795. [Class 98 (ii)] In the preparation of a photographic stencil forming a etching resist, a silver salt emulsion layer is subjected to at least two separate image development steps and to at least two separate steps for imagewise removal of the layer. An image-development step may be performed simultaneously with an imagewise removal step. Two or more latent images may be printed into the layer before any one is developed or firstly one can be printed and developed and subsequently another can be printed and developed. With two images, one image may be developed and the layer removed imagewise and then a second image may be developed and the layer again removed imagewise, or the images ma.y be successively developed and then the layer successively removed imagewise. A developing solution comprising hydroquinone, potassium metabisulphate, potassium bromide, potassium hydroxide, and water used at 100-120‹ F. develops the exposed parts of the emulsion rapidly, tans the gelatine at those parts, and washes out the unexposed parts. In example 1, a silver-plated copper plate coated with an unhardened process-type gelatino-silver halide emulsion is exposed to a positive of an image to be deeply etched and is developed in non- tanning developer. The image is treated in a bleach-hardening bath, the unhardened gelatine is washed out in hot water, and the layer is dried in non-actinic light. The plate is etched deeply with alcoholic ferric nitrate and is washed. The emulsion is exposed to a negative image of the fine detail image, is developed to give a gelatine stencil containing a silver image, is treated in an etch-bleaching bath to imagewise remove the gelatine layer, and a shallow etching treatment is applied. In example 2, a glass plate coated with a hardened processtype emulsion is exposed to a negative image of the image to be deeply etched, is developed, washed, and treated in an etch-bleach bath. After washing, the layer is re-exposed to a negative image of the second desired image, is developed, dried, re-swollen in a solution of a loading agent, e.g. a 20 per cent aqueous solution of sugar or glycerine, the glass etched by sand-blasting, the layer washed, the second image etched from the layer by an etch-bleach bath, the layer retreated with a solution of a loading agent, and the glass given a further light sand-blasting. The cycle of operations may be repeated by washing, bleaching, washing, re-exposing, developing, and etch-bleaching. In example 3, a surface coated with unhardened emulsion is exposed, developed, treated in a bleach-hardening bath, re-exposed to the second image, developed in a non-tanning developer, the unhardened gelatine washed out to give a stencil of the first image only, the second image treated with an etch-bleaching bath, and the surface etched. The surface could also be partially etched between the two imagewise removal steps.