Patent GB-440032-A (GB)
Title: Improvements in and relating to colour photography
IPC: G03C7/24
Filed: 1934-06-15
Abstract: 440,032. Colour photography. KODAK, Ltd., Kingsway, London.-(Eastman Kodak Co. ; 343, State Street, Rochester, New York, U.S.A.) June 15, 1934, Nos. 17743 and 32441. [Class 98 (ii)] A photographic element having superimposed on the same side of a single support at least three gelatine-silver halide emulsion layers containing superimposed latent image records of different colour sensations substantially covering the whole of the visible spectrum is processed to a natural colour photograph by producing reversed silver salt images in all the layers, simultaneously rendering all the images developable, preferably by exposure to light, and thereafter processing each image to the minus colour of the primary colour of which the image is a record. A film may comprise a support of cellulose acetate or nitrate carrying layers of red-sensitized emulsion, colourless gelatine, green-sensitized emulsion, decolourable yellow coloured gelatine and blue-sensitive emulsion. The green sensitizer may be eythrosin and the red naphthocyanol. Suitable yellow dyes are tartrazine, quinoline yellow or brilliant yellow. Colourless gelatine layers may be disposed between the yellow layer and the emulsion layers. The colourless layer between the red- and green-sensitized emulsions may be replaced by a red layer, and the bluesensitive emulsion may contain yellow dyestuff. Gelatine-silver bromide emulsions are employed. The film is slightly hardened, developed in the dark with a metol-hydroquinone developer containing potassium thiocyanate and formaldehyde, washed, treated in a reversing bath containing potassium permanganate and sulphuric acid, washed, in a sodium bisulphite cleared bath, washed, exposed to white light, colour developed to minus red with a developer containing p-aminodiethylanilinehydrochloride, potassium thiocyanate, and m - hydroxydiphenyl, fixed, washed, and thoroughly dried. Further processing is carried out in the light. The top two layers are bleached in a bath containing quinone, hydrobromic acid, glycerine and iso-propyl alcohol or containing chromic acid and methanol, and the film is immersed in a stop bath containing sodium bicarbonate, glycerine and iso-propyl alcohol or containing sodium bisulphite. The top two layers are colour developed to minus red in a developer containing 2-amino-5-diethylaminotoluene-hydrochloride, potassium thiocyanate, p-nitrophenylacetonitrile, and iso-propyl alcohol, and the top layer is rebleached and the silver therein reconverted to silver halide as above described. The top layer is then colour developed to minus blue in a developer containing p-aminodimethylaniline sulphate, 4- nitroacetoacetanilide, and iso-propyl alcohol. The metallic silver is removed by Farmer's reducer and the film is washed and dried. In a modification, the top two reversed silver halide images in the dried film are developed in a hydroquinone-potassium hydroxide developer containing a large amount of sodium sulphate. Development is arrested in a stop bath containing sodium sulphite and acetic acid at 0-5 C., and the upper two layers are fixed. The reversed silver halide image in the bottom layer is colour developed to minus red and fixed. The silver images in the outer two layers are bleached in a potassium ferricyanide bath, and the silver ferrocyanide images colour developed to minus green. The film is washed and dried, and the upper layer is rebleached and colour developed to minus blue. Alternatively, the upper silver ferrocyanide image is redeveloped to silver, the lower silver ferrocyanide image colour developed to minus green and the upper layer rebleached and colour developed to minus blue. In another modification all the reversed images are developed and fixed and the film is dried. The top silver image is bleached and colour developed to minus blue and the silver removed. The other two layers are similarly treated. In a further modification all the reversed images are colour developed to minus red and fixed and the film is dried. The upper two images are bleached, the to image developed to silver, the lower image colour developed to minus green, and the top image rebleached and colour developed to minus blue. In a further modification the top image is colour developed to minus blue in a colour developer containing iso-propyl alcohol as a loading agent, and the lower two images are successively colour developed to minus green and minus red respectively, the film being thoroughly dried before each development. In a further modification the top image is developed to silver and the lower two images successively colour developed. The film is fixed and the top silver image bleached and colour developed. In all modifications the silver is finally removed. When two images have been colour developed, the third silver image may be coloured by mordanting and dye-toning. Reversed images may be rendered redevelopable by treatment with chemical reagents. The emulsion layers may be coated on paper to enable the picture to be viewed by reflected light. The film may carry a sound track. Specifications 176,357, 245,198, [both in Class 98 (ii)], 341,183, 376,838, 427,472, 427,516, 427,518, and 427,520 are referred to.