Patent GB-404856-A (GB)
Title: Improvements in the photographic production of multi-colour pictures
IPC: G03C7/26
Filed: 1933-05-17
Abstract: 404,856. Colour photography. I. G. FARBENINDUSTRIE AKT.-GES., Frankforton-Main, Germany. May 17, 1933, No. 14322. Convention date, Feb. 3. [Class 98 (ii).] In the production of multicolour photographs or kinematograph films in which colour-record components are produced in super imposition in the same silver halide emulsion layer, an unfixed, chemically-toned print is first made from one component negative, and before printing the remaining component negatives the sensitivity of the unchanged silver halide is restored by means of a reducing agent, such as a sulphite, which does not reduce silver bromide, sodium sulphite or bisulphite, potassium metabisulphite, hydrazine sulphate and hydroxylamine being mentioned. Sensitive material may be used provided with an emulsion sensitized for one spectral region and dyed with a filter dye which is removable or decolourisable in the subsequent treatment (e.g. development), and is of a colour complementary to that of said region ; and the material may have such a dyed emulsion on each side, the two emulsions being sensitized for different colours. In examples (1) a film for two-colour work, bearing an ordinary emulsion layer dyed yellow, is exposed from the layer side behind a red-record negative and developed but not fixed, and the image is toned blue with a bath prepared from potassium ferricyanide, sodium bichromate, iron ammonium alum and oxalic acid ; the sensitivity of the unchanged silver halide is restored with sodium sulphite, and the layer is exposed from either side behind the blue-record negative, developed with an acid developer such as amidol, and fixed, and the silver image is first bleached with a bath containing potassium iodide, iodine and acetic acid, and then dyed orange with a mixture of auramine and fuchsine ; (2) a film for threecolour work bearing on one side an emulsion as in (1), and on the other side a green-sensitive emulsion dyed red, is exposed simultaneously to the green-record and red-record negatives, developed but not fixed, and the print on the ordinary emulsion from the red record is toned blue as in (1) as by flotation ; after reviving the layer with potassium metabisulphite, the unchanged silver halide is exposed behind the blue-record negative, and through the bluetoned image, preferably to green-blue light, developed with an acid developer and fixed, and the silver images are first bleached with a bath prepared from copper sulphate, acetic acid, potassium sulphocyanide and saltpetre, and are then dyed as by flotation or coating, that from the blue record with auramine and that from the green record with fuchsine: (3) a film as in (2) is exposed to green light, under the redrecord negative, from the side bearing the ordinary emulsion, in order to produce a print in the support-side of the green-sensitive layer, and then to blue light under the green-record negative to produce a print directly on the ordinary emulsion layer; after developing, without fixing, the print from the red record is toned blue as in (2), and the film is revived with a bath of hydrazine sulphate and citric acid ; the blue-record negative is printed by green light directly on the green-sensitive layer, and the image is developed in an acid developer and fixed, the two silver images being then bleached and coloured as in (2) : (4) a film bearing on one side a red-sensitive emulsion dyed green, and on the other side a greensensitive emulsion dyed red, is exposed to green light, under the green-record negative, from the red-sensitive side, and, simultaneously or not, to red light, under the red-record negative, from the green-sensitive side, and is developed without fixing ; the print from the red record is toned iron blue, and the other print is copper bleached as in (2), treatment in each case being confined to one side ; after reviving the layers with potassium metabisulphite, the blue-record negative is printed directly on the layer containing the blue-toned image, and a grey key image is printed directly on the other layer, the film is developed with an acid developer and fixed, the print from the blue-record negative is copper-bleached as in (2) and dyed yellow with auramine, and the previously-bleached print from the green-record negative is dyed red with fuchsine, the grey-key image in the same layer remaining unaffected. Tartrazine, Rapid Filter Red, Rose Bengal and Filter Green are mentioned as filter dyestuffs, and formulae are given for the developing, reviving, bleaching, and toning baths.