Patent GB-381787-A (GB)
Title: Improvements in or relating to the production of photographic relief images
IPC: G03C5/315
Filed: 1931-12-24
Abstract: 381,787. Photographic gelatin relief images. KODAK, Ltd., Kingsway, London. -(Assignees of Seymour, M. W. ; Kodak Park, Rochester, New York, U.S.A.) Dec. 24, 1931, No. 35650. Convention date, Dec. 27, 1930. [Class 98 (ii).] Wash-out gelatin relief images which adhere firmly to the original support, and which may be used for producing monochrome prints on paper, colour photographs, or for imbibition printing &c. are prepared in an emulsion layer whose sensitivity to light varies from a maximum on the side adjacent to the support to a minimum on the other side by printing the image from the less sensitive side, treating the layer to harden it differentially in accordance with the differential density of the printed image, and washing out the unhardened parts of the layer. The invention is described in connection with a silver halide emulsion layer, for example a gelatino-silver bromide-iodide layer, which may be treated to produce the above-stated sensitivity gradation either (1) by treating its free surface with a solution of an agent which has the property of de-sensitizing the silver halide or rendering it incapable of being developed, for example, potassium iodide, de-sensitizing dyes, such as pinacryptol green or phenosafranin (preferably in alcoholic solution), or inorganic oxidizing agents such as iodine dissolved in a solution of ammonium bromide, chromic acid, and cupric chloride ; or (2) by coating the support, before applying the sensitive emulsion, with a sensitizing dye, such as orthochrome T, ethyl red, isoquinoline red, or naphthacyanol, dissolved in a water solution of gelatin. In either case, the agent diffuses into the sensitive layer from one side, and its effect on the silver halide diminishes from that side to the other. In the second case, printing must be performed with a light consisting mainly of rays to which the layer is hyper-sensitized by the dye. To produce the relief, the printed layer is either (1) developed with a developer having poor tanning properties, such as hydroquinone containing caustic soda, and then treated with a bleaching bath, preferably one containing an acid oxidizing agent and a soluble halide (e.g. ammonium bichromate, sulphuric acid and sodium chloride), which hardens the gelatin in proportion to its content of metallic silver, whereafter the unhardened gelatin is washed out with warm water and the bleached silver image may be removed by hypo ; or (2) developed with a strongly tanning developer, such as pyro containing little or no sulphite, hydroquinone or paraminophenol, which produces similar differential hardening during development, and washing out with warm water. The second method is preferable when the gelatin relief is to be used for imbibition printing, and in this method also the layer may be treated with a bleaching bath after the tanning development but before washing out, whereby the insolubility of the image portions is still further increased. Two-colour kinematograph films may be produced by the above-stated process on film stock coated with emulsion of graded sensitivity on both sides, the component colour-record reliefs being produced on opposite sides and separately dyed by flotation.