GB392785A - Improvements in photographic reliefs - Google Patents

Abstract

392,785. Photographic reliefs. TECHNICOLOR MOTION PICTURE CORPORATION, 110, Brookline Avenue, Boston, U.S.A.-(Assignees of Troland, L. T. and Eaton, R. D. ; 110, Brookline Avenue, Boston, U.S.A.) Aug. 18, 1932, No. 23190. Convention date, Sept. 4, 1931. Drawings to Specification. [Class 98 (ii).] A photographic gelatine relief, particularly for imbibition printing, comprises substantially interconnected image-forming elements of dyeabsorbing gelatine embedded in a body of relatively non-dye-absorbing gelatine having approximately the same thickness at any point of the relief, the surface of the relief being substantially smooth. Such a relief is obtained by developing a silver halide emulsion with a hardening developer, e.g. pyrogallol or pyrocatechin, without reducer, and then subjecting it to a controlled oxidation treatment to oxidize the unexhausted developer in such a manner as to produce a body of non-dye-absorbing but relatively soluble gelatine filling the spaces between the particles of developer-hardened gelatine. Oxidation may be effected by vigorous washing in water containing dissolved air, or by oxidizing agents such as potassium bichromate or ferricyanide ; oxidation being controlled by regulation of the length and pH of the oxidizing wash, the concentration and pH of the bichromate or ferricyanide, and the pH of the developer. In an example, an exposed film is treated in a continuous developing machine for 3¢ minutes at 64‹ F. in a developer comprising 0-8 per cent pyrogallol, 0-3 per cent sodium hydroxide, 0-15 per cent ammonium chloride, 0.15 per cent potassium bromide, and 0-02 per cent citric acid. After development, the film is passed to a wash tank through which water is circulated so as to be changed completely in about 10 minutes, the water entering at 64‹ F. with a pH of 6-5. The film is treated for 2 minutes and is next treated for 1¢ minutes in a bath of ferricyanide of 14 per cent strength, kept at a pH of 3-7 and a temperature of 65‹ F., which oxdizes any remaining developer and bleaches the silver image. After a further wash for 1¢ minutes in water at 65‹ F. and with a pH of 6-5, the film is fixed by treatment in a non-acidic sodium thiosulphate solution of normal strength and then etched by water at 130‹ F.