GB406663A - Improvements in or relating to colour photography - Google Patents

Abstract

406,663. Colour photography. BAKER, T. T., The Hut, Hatch End, Middlesex, and DUFAYCOLOR, Ltd., 19, New Bridge Street, London. Aug. 29, 1932, Nos. 24136/32 and 17733/33. [Class 98 (ii).] A method of producing a composite coloured print from a master colour-screen record having two or more part images corresponding to the colours of the screen comprises the steps of preparing two prints from two of the part images, one being on a light-reflecting base, such as paper, and being coloured, e.g. by toning, in a colour complementary to the colour of the corresponding record, and making from the other print an undeveloped gelatin print pigmented in a colour complementary to the colour of the corresponding record, superposing this print in register on the first print and developing it. For the third print in the case of three-colour records, a print is made on a strippable base, coloured in a colour complementary to the third record, applied in register to the first print, and the base stripped off. A positive is first prepared by reversal from a negative on a film bearing a screen of red, green and blue elements. Two holes are punched in the film for registration purposes and it is printed in succession on to three pieces of bromide paper sensitized respectively for blue, green and red and having similar registration holes, the transparency being reversed when making the red print. The colour of the printing light used corresponds in each case to the colour of the elements of the negative to be printed. The time of exposure may be determined by measuring the density of the negative by means of a light sensitive cell. The prints are then developed and reversed and the print on blue sensitive paper is toned yellow, e.g. with lead acetate and potassium ferricyanide followed by treatment with potassium bichromate. The print on green sensitive paper is printed on pigment paper, for example, that known under the Registered Trade Mark '' Carbro," and the pigment image is applied to the yellow toned print and developed. The third print is made on a paper with a strippable backing and toned blue, e.g. with ferrocyanide and iron alum, and is applied to the superposed prints. Each print is provided with a third hole and a registering board having three upstanding pins is used to facilitate register. In a modification, the third print is made on a celluloid backing which is not stripped off. In a further modification, two prints only are used and are exposed in superposition using a yellow filter, e.g. one dyed with the ammonium salt of aurophenin, or uranin. The three prints may also be made simultaneously if a known type of light-splitting device is used, the prints being made under appropriate filters on a single paper strip coated with a panchromatic emulsion. Specifications 175,003, 198,745, 217,557 and 322,432, [all in Class 98 (ii)], are referred to.