GB203358A - Improvements relating to colour photography and the like - Google Patents

Abstract

203,358. Hamburger, A. March 7, 1922. Colour photography; toning. - A method of dye-toning a positive or negative image, which may be employed to produce the elements of a multi-colour photograph, consists in treating the image simultaneously or successively with selected dyes of different colours, which impart to the image a range of tones extending from one colour to the other. In one example, as applied to the production of a multi-colour kinematograph film, two component negatives are made (1) for the green and blue-violet on a film treated with erythrosine and exposed without a light filter, and (2) for the red, orange and yellow on a film treated with pinacyanol and exposed through a red or red-orange filter. Positive prints are made from these, preferably on opposite sides of the same film. A mixture of rhodamine B and auramine is then applied to the positive from film (1), and a mixture of malachite green, xylene red, and brilliant green to the positive from film (2). Or, the dyes may be applied in succession to the appropriate positives. The positive film is bleached' in a solution containing chromic acid, potassium ferricyanide, and thiocarbamide, and washed to clear the highlights, either after the dyes have set, or before applying them. The positive from film (1) then exhibits a gradation from red to yellow, and the positive from film (2) a gradation from green to blue, the whole therefore giving the effect of a four-colour process with a greyish key due to the bleached silver image itself. The concentration of each dye is so chosen that sufficient dye is applied to saturate the portions of the image which represent the colour of that dye. In a modified process, the silver image is removed from the film to be dyed, leaving only gelatine differentially hardened', and the dyes used are acid yellow and acid magneta for the first positive, and crystal violet and azo blue for the second. Negatives from which the silver has been removed may be similarly treated, for example by the use of dyes of the pinatype series.