Patent GB-553952-A (GB)
Title: Production of multi-colour photographic images
IPC: G03C7/26
Filed: 1941-10-17
Abstract: 553,952. Colour photography. TULL, A. G. Oct. 17, 1941, No. 13387. [Class 98 (ii)] An exposed multilayer or multistrata silver halide emulsion coated material is colour processed by developing the latent images, forming in two or more of the layers or strata silver salt or silver salt complex images having an acid radical which renders the images capable of being chemically toned and surrounded by complementary deposits of silver or silver halide, applying a chemical toning bath containing two or more different chemical toning reagents to form two or more different chemically toned images from two or more of the toneable images, and producing a colour developed image of another colour in another layer or stratum. With a three-layer material, two different chemically toned images may be produced simultaneously in the outer and middle layers, and the colour developed image in the lowermost layer. The blue-sensitive layer may be the top or the bottom layer, the material in the latter case being exposed through the transparent support. In reversal processing the first developer contains a silver halide solvent, e.g. KCNS. In negative processing the silver images in at least the two layers nearest the surface are, without fixing, bleached to silver ferrocyanide (which can later be converted to a complex image by treatment with thiourea), and in reversal processing the residual silver halide in at least the two outer layers is converted, without removing the developed silver, into a salt or complex image capable of being chemically toned, e.g. by bathing in a bath containing thiourea and a salt-forming reagent as described in Specification 540,970. All or only the top two layers may be treated. In the latter case, anti-swelling or thickening agents, e.g. inert salts, water-miscible organic solvents, sugar, or glycerol, may be added to the baths. Alternatively the time of action or concentration of the baths is controlled. The chemically toned images may be produced as described in Specifications 540,971 or 552,230. The mixed toning bath may comprise a ferric salt, a uranium salt, nitric acid, and potassium bromide, giving a Prussian Blue image in the top layer and a uranium ferrocyanide image in the middle layer. If there is a ferrocyanide image in the bottom layer, the action is confined to the top two layers. The image in the bottom layer is colour developed by a colourforming developer with or without a colour coupler. Prior to colour development, developable silver salts in the top two layers only previously removed either by treatment with relatively concentrated hypo, by treatment with a fixing bath containing antiswelling or loading agents, or by treatment in an iodizing bath containing hypo, sodium sulphite, and potassium iodide. In negative processing, the material should be processed in the dark. A reagent preventing development at a surface layer or stratum, e.g. KI or hypo, may be added to the colour developer The concentration of alkali in the colour developer is reduced to a minimum, and the use of sodium carbonate avoided. The colour 'of decolourized Prussian Blue and uranium ferrocyanide image may be restored by treatment with ferrocyanide solution containing acetic acid. Examples 1 to 4 illustrate such methods. A chloride or ferrocyanide may be used in the toning bath to give silver salt which can be removed by sodium sulphite, ammonium sulphite, or ammonia. True-or false-colour records may be produced, various arrangements of the layer sensitivities and the colours of the respective images being referred to. A green-absorbing filter may be provided between the green- and red-sensitive layers. A scheme for the selection of appropriate exposure and copy materials is specified. Stripping material may be employed in which the emulsion layers may be transferred to a new support prior to processing or colouring. Specifications 458,400, 505,834, 540,975, 540,979, 541,355, 541,545 and 553,962 also are referred to.