Patent GB-222523-A (GB)
Title: Direct colour photography
IPC: G03C7/46
Filed: 1923-04-05
Abstract: 222,523. Martinez, M. April 5, 1923. Colour photography; plates, films, and papers ; emulsions and sensitive coatings, preparing; developing.-The process involves the exposure of a surface comprising particles of a sensitive coloured metallic compound and subsequent treatof the surface which leaves particles of their original colour at those places which have been illuminated by light of that colour and removes or alters the coloured particles at places which have not been so illuminated. Usually two or more differently coloured compounds are used in the surface. The particles are preferably held in a vehicle, such as gelatine, collodion, gums, resins, or starch, which is not coloured by them or by any constituent of them, the vehicle being colourless except when it is given a general stain, as when protection is desired against violet or ultra-violet rays. Examples are given in the Specification of the preparation of sensitive coloured compounds utilizing- silver, mercury and iron salts, but compounds of other metals, such as uranium, may also be employed. Examples are also given of developing compositions, with formulae. The silver compounds may be prepared by interaction of silver salts with dye-stuffs, or with the alkali chromium oxalates. Where two or more coloured sensitive compounds are used they may be formed, generally by precipitation, one after another in the same vehicle or on the same support, and may then be rendered more sensitive by ripening. Alternatively each compound may be prepared separately and may be ripened by exposing for some time, usually one half to one hour, to light of its own colour, of feeble luminosity but of intense colour and at a temperature of 25-30‹ C. The differently coloured compounds are then mixed in the required proportions. If particles of coloured silver compounds are used, the particles altered will, after development in the ordinary way where transparencies &c. are desired, be blackened, and the image will be visible in colours. The unaltered silver particles may then be fixed with hypo, or where this is not advisable by treatment simultaneously with or subsequent to development, with iodine or an iodide or both. Preferably however the image is reduced after development with for instance hydrogen or sodium peroxide acidified with a little hydrochloric or sulphuric acid. For prints or the like, the image is treated directly to make the light-altered portions white for example by immersion in a solution of potassium ferrocyanide preferably mixed with potassium oxalate or tartaric acid, with or without a salt of a metal giving a white ferrocyanide, or the blackened particles produced by ordinary development are whitened, preferably by conversion into a white ferrocyanide. The whitened picture is fixed by means of a solution cf ammonium iodide and iodine which may be added to the developer. When sensitive iron particles are used, the ferrous compounds produced on exposure may be dissolved out on washing by manganese salts, or salicylic or benzoic acid or alkali salts thereof, which may be incorporated in the emulsion or applied as a preliminary coat.ng to the support. In the emulsion, dyestuffs or other coloured substances may be used the colours or tints of which are alterable by reagents such as acids or alkalis, thus enabling the finished photograph to be altered or corrected.