Patent GB-694580-A (GB)
Title: Multi-coloured photographic prints
Inventor: LAWES LOUIS FREDERICK WILLIAM
IPC: G03C5/18
Filed: 1950-10-17
Abstract: 694,580. Photographic diazotype process. LAWES BROS., Ltd. Oct. 12, 1951 [Oct. 17, 1950], No. 25317/50. Class 98 (ii). In a printing process of the type wherein material, light-sensitized with a diazo, tetrazo, or other nitrogen-containing compound capable of coupling with a coupling compound to form a coloured compound and releasing nitrogen under light action to form a colourless decomposition product, is exposed under an image-bearing transparency and developed with a solution of a coupling component, a selected unexposed portion or portions of the material is treated with a coupling component or components to produce areas in a required colour or colours, and the whole or the remaining unexposed portion or portions of the material are treated with another coupling component adapted to produce another colour or shade of colour, preferably a dark or unobtrusive colour). The diazo compound may be one which forms a dye with a coupling component in acid or neutral solution, one which requires the application of heat to the print or the use of a heated developer or both, or one which requires the use of an alkaline solution of a coupling component. Light-sensitive paper may be exposed through a transparency carrying a plan or map, and developed, the area of the plan or map to be coloured cut out of the print and registered with the corresponding area of the transparency, and a second light-sensitive paper exposed through the combination. The masked area of the second paper is developed using a coupling component which produces the desired colour, and the whole of the paper is developed with a different coupling component to produce the remaining lines in a different colour. The first paper may have a semi-transparent support to produce only partial masking. The coupling component may be applied by brushing, dabbing, or spraying, or by rollers, and the stencil formed from the first paper by the cutting out of the mask may be used to facilitate the local application of the coupling component. In an example, a paper, film, or cloth support is coated on one or both sides with a diazotype sensitizing composition consisting of an aqueous solution of the zinc chloride double salt of diazotized 1 - amino - 2: 5 - diethoxy - 4 - benzoylaminobenzene, thiourea, citric or tartaric acid, and naphthalene-1: 3: 6-trisulphonic acid. The material is exposed under a transparency and developed to black, blue, brown, or other dark colour, and cut-outs are made corresponding to the selected areas to be coloured and attached to the transparency. Similar diazotype material is exposed under the masked transparency, and these masked areas are treated with a developer comprising an aqueous solution of tartaric (or citric or boric) acid, potassium citrate (or sodium citrate, formate, acetate, or benzoate), and saponin, to which has been added as coupling component 1-phenyl- 3-methyl-5-pyrazolone, resorcinol, acetoacet. anilide, 2: 3 - dihydroxynaphthalene, 2: 7 - dihydroxynaphthalene, or phoroglucinol, or mixtures thereof. The print is then developed in a similar developer.