Patent GB-639182-A (GB)
Title: Processes for producing multicoloured subtractive positive prints
IPC: G03C7/26
Filed: 1945-03-19
Abstract: 639,182. Photographic colour printing processes. TRIMBLE, L. S. March 19, 1945, No. 6860. Drawings to Specification. [Class 98 (ii)] A process for producing multicolour subtractive positive prints includes the steps of (a) printing at least one component positive image on a photographic silver halide material from a colour separation negative or negatives, not more than one image being printed on either side of the material ; (b) developing the image or images ; (c) treating said image or images with a non-bleaching aqueous solution comprising 2-3 grams of an alkali metal bichromate and 1-2 grams of an alkali metal chloride or bromide in each 100 grams of water ; (d) printing one other component positive image from a further colour separation negative through and in register with one of said images and the corresponding negative from which it was printed, said image and negative forming a uniform neutral density mask, by locating the further colour separation negative between the photographic material and the said corresponding negative with the image bearing layer of the further negative in contact with the emulsion layer of the material ; (e) developing said other component positive image and converting it to a suitable colour by means of treating solutions, such as toning and bleaching baths, of low oxidation or reduction potential, and (e) converting said first mentioned image or images to a suitable colour or colours. In the example given a three colour positive kinematograph film is produced by printing on opposite sides of a support bearing an emulsion layer on each face from green and blue colour separation negatives, developing the images to silver and after washing immersing the film in a bath containing 2-3 grams of potassium dichromate and 1-2 grams of potassium bromide per 100 grams of water and of pH greater than 3.5. The sound track is printed from the red record negative with ultra-violet light on the side carrying the blue record positive silver image and the red record is placed between said image and the blue record negative which between them form a uniform mask and a print made by stepping up the exposure. The red record image is then developed, washed, chemically toned to prussian blue, and the film is then washed and fixed in a non-hardening hypo bath containing sodium sulphite or bisulphite. The green and blue record images are coloured respectively magenta and yellow, either by chemical toning, e.g. to nickel dimethylglyoxime and cadmium sulphide, or by a mordant dye process using a floatation method. Formulµ are given for a prussian blue toning bath and an iodine mordanting bath. Two images may be printed on one emulsion by the method of the invention and the third image printed by imbibition, for example in the case of a film having emulsions on opposite sides of the support on the opposite face to the first two images. Instead of immersing the film in the solution which protects the two silver images against subsequent treating solutions, as described above ; it may be floated on the solution, a further image printed on the treated side, and the three images separately toned by floatation.