Patent GB-551008-A (GB)
Title: A photographic material for colour photography and kinematography
IPC: G03C7/26
Filed: 1939-04-14
Abstract: 551,008. Colour photography. MOEN, L. April 14, 1939, No. 11344. [Class 98 (ii)] Multilayer material for colour photography comprises three or more superimposed silver halide emulsion layers and a layer which is to be rendered opaque during the processing and which contains a silver salt which is to be converted to a uniform, relatively opaque silver deposit during the processing and at least partially at a development stage other than the stage of development of the latent images in the emulsion layers. The layer may be the middle emulsion layer of a three-layer material, and then contains, in addition to any colour sensitizer in that layer, an infra-red sensitizer which enables the layer, after development of a latent image therein, to be re-exposed with infra-red light and developed with a colour developer giving a uniform silver deposit consisting in part of the developed latent image and in part of the developed residual halide, in addition to a reversed colour image formed by colour development of the residual halide. Alternatively, a separate layer may be used which may consist of a silver bromide or chloride emulsion sensitive to infra-red, or which is a silver iodide emulsion. The intermediate layer may be infra-red sensitized with Kryptocyanine, or may consist of an emulsion inherently sensitive to infra-red. The material may comprise a support of celluloid, cellulose derivative, or glass, carrying a green or red sensitive layer, a first intermediate layer, which may be coloured green, red, or yellow, a red or green sensitive emulsion, a second intermediate layer preferably containing a yellow filter dye, and a top blue sensitive emulsion layer. After exposure, the material is developed in a negative developer or in a developer containing a silver halide solvent such as potassium thiocyanate the filter dye is washed out, and the material is exposed from both sides to infra-red light and is re-developed to produce, a dense silver deposit in the intermediate layers. The outer layers are successively re-exposed and colour developed, and the residual silver halide in the middle layer is rendered developable either by exposure to strong light, or by treatment with a fogging agent such as thiosinamine, thiourea or very dilute silver nitrate, or by treatment in a bath removing or bleaching silver without affecting silver halide, e.g. Haddon's reducer, weak chromic acid solution, or a solution containing copper sulphate, alum, and sodium chloride, followed by diffuse exposure to light. The middle image is colour developed and residual silver or silver salts are removed with Farmer's Reducer. Intermediate layers containing fogged silver iodide are not affected by a normal first developer and may be blackened afterwards with acid amidol. The rear intermediate layer may be omitted, and the colour sensitizer in the rear emulsion layer may be such that it is unaffected by normal processing. The rear layer may then be selectively exposed with coloured light, and colour developed. Alternatively, the rear intermediate layer may comprise a fogged silver bromide emulsion which is blackened in the first development. A dye-mordant such as zinc ferrocyanide, a tannate, a fatty acid of high molecular weight, or a salt thereof, may be incorporated in the front intermediate layer, and a filter dye such as Auramine, Quinoline Yellow, Thioflavine, or Phosphine mordanted thereon. A dye such as o-amino-p-nitrophenol which can be rendered colourless in a solution of suitable pH value may be used. Dyes readily decomposed by reagents such as weak acids may also be used. A filter dye may be incorporated in the rear intermediate layer in a similar manner. Separate filter layers may be provided, or the filter dyes may be incorporated in the appropriate emulsion layers. Controlled re-exposure may be effected after the first development step, the developed image in one layer acting as a mask for a corrective exposure in a following layer. The material may be used in a non-reversal process in which after exposure the material is developed to give negative silver images, is given a diffuse exposure with infra-red light to fog the intermediate layers which are then developed, and is fixed. The silver is bleached to a silver salt incapable of redevelopment without re-exposure, e.g. in a bath containing ammonium persulphate and potassium bromide or containing a free halogen and a bromide. The material is again exposed to infrared light and is developed to produce opaque intermediate images, after which the material is processed by successive re-exposure and colour development, developed silver being finally removed with Farmer's Reducer. The infra-red sensitizer must withstand the action of the developing and bleaching baths, or an inherently infra-red sensitive emulsion may be used. With a fogged silver iodide intermediate layer, the unaffected silver bromide may be removed without affecting the silver iodide with a 40 per cent hypo bath, after which the silver images are bleached and the silver iodide developed with acid amidol. The material is then processed by successive reexposure and colour development. With material in which the intermediate layers containing silver salt are omitted and the middle emulsion contains an infra-red sensitizer such as Kryptocyanine in addition to the ordinary red or green sensitizer, intermediate filter layers being provided, after the first development the residual halide in the middle layer is fogged with infrared light, and the material is developed in the colour developer appropriate to the middle layer. The outer layers are successively re-exposed and colour developed, and developed silver and residual silver halide is removed with Farmer's Reducer. Specification 505,099 is referred to.