GB270386A - Improvements in or relating to photographic processes - Google Patents

Abstract

270,386. Wade, H., (Wadsworth Watch Case Co.). Feb. 4, 1926. Plates and films; sensitive coatings, preparing. -A sensitive medium for photographic or photomechanical use is prepared by incorporating in selected sensitive portions of asphaltum which form the main base of the medium, a sensitizer which liberates a halogen on exposure to light, such as a metallic halide and a halogen-substituted hydrocarbon. The medium may be used in the production of screenless grained litho plates, monochrome or colour-record intaglio, relief, or halftone printing-plates, or for line engraving on zinc, copper, &c. It renders possible the production of printing-surfaces from continuous tone negatives without resource to aquatint grain, reticulation, screens &c. Exposure is effected under an arclamp in from one half to four minutes. In an .example, a coating is prepared containing asphaltum, solvent naphtha, benzine, and a sensitizer comprising ethyl methyl ketone, iodoform, solvent naphtha and ammonia, all in stated proportions, and is applied to a grained or smooth surface. A similar sensitizer including also lead triethyl iodide may alternatively be used. After exposure to an image by contact or projection, development is effected by rubbing with a mixture of oleic acid and white mineral oil to remove the unexposed portions of the layer, followed by rinsing with dilute ammonia and water. In a further example, the coating comprises hydriodic acid, iodoform, asphaltum, and a small quantity of ammonia which is added to stabilize the coating, but is preferably neutralized before exposure. Specification 203,285 is referred to.