Patent GB-447092-A (GB)
Title: Improvements in and relating to colour photography
IPC: G03C7/30
Filed: 1934-11-10
Abstract: 447,092. Colour photography. KODAK, Ltd., Kingsway, London.-(Eastman Kodak Co. ; 343, State Street, Rochester, New York, U.S.A.) Nov. 10, 1934, No. 16012 /35. Divided out of 440,032. [Class 98 (ii)] A process for the production of a photographic record in the minus colours of the original by converting into coloured image records superimposed latent image records of different colour sensations covering substantially the whole of the visible spectrum which have been produced respectively in at least three gelatino - silver halide emulsion layers inseparably coated on the same side of a single support by a single exposure of all the layers from one face whereby such latent images lie accurately superimposed and mostly in the corresponding strata of each layer, includes simultaneous colour development of the silver salt images in at least two layers and subsequent bleaching of less than all of the colour developed images to decolourize the colour and reconvert the silver which was developed therewith into a silver salt image or images. The film comprises a cellulose acetate or nitrate support having superimposed thereon thin layers of emulsion sensitized to red with naphthocyanol, colourless gelatine, emulsion sensitized to green with erythrosin, decolourable yellow gelatine coloured with tartrazine, quinoline yellow or brilliant yellow, and blue sensitive emulsion. The gelatine of the film to be processed is hardened, the images in all the layers are developed to minus red using a colour developer containing p-aminodiethylaniline hydrochloride and m-hydroxydiphenyl the film is fixed, washed, and dried. Alternatively, the film is developed in an ordinary developer containing formalin, fixed washed bleached in an ammoniacal ferricyanide or hydrobromic acid oxidizing bath, and redeveloped in a minus red colour developer. The two outer layers are bleached in a bath containing quinone, hydrobromic acid and loading agents such as glycerine and isopropyl alcohol. The film is immersed in an alkaline alkaline stop bath and washed, and the images in the upper two layers are colour developed to minus green in a developer containing 2 - amino - 5 - diethylaminotoluene hydrochloride and p-nitrophenylacetonitrile. The film is washed and dried. The uppermost layer is bleached and colour developed to minus blue in a developer containing p-aminodimethylaniline sulphate and 4-nitroacetoacetanilide. The metallic silver is removed with Farmer's solution, and the film is washed and dried. The developers may contain potassium thiocyanate to increase the reduction potential. In a modification, the upper two latent or bleached images only are developed by the use of a hydroquinone-potassium hydroxide developer containing a high concentration of sodium sulphate as loading agent. Development is arrested in a stop bath containing sodium sulphite and acetic acid at 32-40 F. Silver salt in the upper two layers is removed, if present, by controlled penetration of a fixing agent. The image in the lowermost layer is colour developed to minus red, and if necessary the lowermost layer is fixed. The silver images in the outer two layers are bleached in a potassium ferricyanide bath, colour developed to minus green, and the film is washed and dried. The upper layer is then bleached and colour developed to minus blue. In another modification, the latent or bleached images are colour-developed to minus red and fixed if necessary. The film is dried, the images in the upper two layers bleached, the image in the top layer redeveloped to silver, the image in the middle layer colour developed to minus green, and the image in the top layer bleached and colour developed to minus blue. Alternatively, the top layer only is developed to minus blue by controlled penetration of a colour developer. The image in the middle layer is colour developed to minus green. Where only one image remains as a silver image this can be coloured by mordanting or dyetoning. Bleached images may be rendered developable by exposure to white light or by treatment with chemical reagents such as are described in Specification. 341,183. The emulsion layers may be coated on paper. The films may carry a sound track. Specifications 245,198, [Class 98 (ii)], 376,838, 427,516, 427,518, 427,520. and 444,198 also are referred to. The Provisional Specification describes also the use of acetone, methyl or ethyl alcohol, and sugars as loading agents for the photographic processing solution, and the use of hydroxylamine or hydrazine in a stop bath for a ferricyanide bleaching bath.