Patent GB-553961-A (GB)
Title: Production of multi-colour photographic images
IPC: G03C7/26
Filed: 1941-12-05
Abstract: 553,961. Colour photography. TULL, A. G. Dec. 5, 1941, No. 15704. [Class 98 (ii)] A multi-colour photographic image is produced on an exposed and developed material having a transparent support carrying two sensitive silver halide emulsion layers on one side and a single silver halide emulsion layer on the other side (none of the layers containing dyes participating in the formation of coloured images) by producing different chemically toned images simultaneously in the two emulsion layers on the one side by means of a toning bath containing two different chemical toning reagents and producing another coloured image in the single emulsion layer either from the residual halide or from developed silver. The material may have a transparent support carrying on one side a single blue-sensitive emulsion layer and on the other successively a greensensitive and a red-sensitive emulsion layer The blue-sensitive layer may contain a dye-component or dye-derivative capable of being converted to dye. A decolourizable yellow filter layer may be provided between the support and the bluesensitive layer, and a blue-green image in the green-sensitive layer or in both positions. A red filter layer may be provided between the green- and red-sensitive layers. The material is exposed from the single-layer side, and is processed by reversal to form a reversed yellow image in the blue-sensitive layer, a magenta image in the green sensitive layer, and a blue-green image in the red-sensitive layer. The material may be printed on to similar material also processed by reversal. Alternatively the original material may be processed to a negative and then printed on to similar material processed to a positive. The latent images may be developed with a developer containing a silver salt solvent, e.g. NH 3  or KCNS, both sides being simultaneously treated either by dipping into a tank or by causing a continuous strip to traverse a tank. The twolayer side is processed by chemical toning in the manner described in Specification 540,971, or in Specification 541,355, and the single-layer side is processed by colour development, chemical toning, dye toning, dye-destruction (diffuse dyeing of the layer being effected after exposure), the silver diazotate process, or by a process relying on the formation of a coloured relief image. In reversal processing, the residual halide in the layers to be chemically toned is converted in a silver ferrocyanide-thiourea complex as in Specification 540,970, e.g. by simultaneously treating both sides of the support and applying the toning bath only to the side to be chemically toned, or by converting the silver halide to the complex on only one side of the support and applying the toning bath to both sides. The complex-forming bath may contain thiourea and potassium ferrocyanide, and the toning bath ferric nitrate, uranium nitrate, nitric acid, and potassium bromide. Toning may be restricted to the two-layer side by using a flotation process, or by applying the toning solution by means of a roller or rollers, or by coating the single-layer side with a waterproof varnish. With individual pictures, a double-hinged developing frame may be used, the material under treatment being placed between the sections so that the sides of the two frames form processing dishes located on the two sides of the material. Alternatively the processing dish may have a layer of adhesive material to which the side of the material not be treated is applied, or a varnish layer of cellulose nitrate or benzyl cellulose may be applied to the side not to be treated. The uranium ferrocyanide image may be converted into a dye-toned image as described in Specification 540,979. The complex image on the single-layer side may be toned to lead chromate by converting the complex image to lead ferrocyanide with a bath containing lead nitrate, nitric acid, and potassium bromide and then treating with potassium chromate solution. Alternatively the complex image may be treated with a bath containing thiourea and potassium chromate, and then treated in a bath containing lead nitrate and nitric acid. If the single-layer side is processed after chemical toning of the double-layer side, the material may be dipped bodily in the thiourea-chromate bath, and the single-layer only treated with the lead nitrate bath. Silver and silver salts are removed by treatment in Farmer's Reducer. After chemical toning of the double-layer side, the residual silver halide in the single-layer side may be converted to a silver iodide mordant, and then bathed in a basic dye. The material may also be dipped into a zinc salt bath as described in Specification 540,979 to form a zinc salt mordant image both in the uranium ferrocyanide toned layer and in the single layer. The zinc salt image in the double-layer side is dye-toned with a basic magenta dye, e.g. Rhodamine, and the image in the single layer with a basic yellow dye, e.g. Auramine. The mordanted dyes are insolubilized, and silver, silver salts, and zinc salts removed with Farmer's Reducer. Alternatively, the single layer may be diffusely dyed after exposure and prior to or after development with Metanil Yellow. The layer may contain prior to exposure a dye precipitant, when the material may be bodily dipped into dye solution. Alternatively, the layer may contain a dye component prior to exposure. A bath containing thiourea, hydroquinone, sulphuric acid, and potassium ferrocyanide may be used simultaneously to destroy selectively the dye in the single layer side and to produce chemically tonable complex images from the residual silver halide in the double-layer side. The double-layer side may be processed as in Specification 541,355 and the single-layer side by chemical or dye toning. Specifications 540,975, 547,722, 551,799 and 553,952 also are referred to. According to the Provisional Specification, the yellow image in the single-layer side may be formed by the process of Specification 547,722. The blue-sensitive layer may contain a dye for the formation of the final colour image.