GB470855A - Improvements in or relating to colour photography - Google Patents

Abstract

470,855. Colour photography. SPENCER, D. A. Jan. 23. 1936, No. 2224. [Class 98 (ii)] A process of developing a negative or positive photograph on multicolour screen material to obtain a developed image which, in the thickness of the emulsion layer, is denser nearer to the support than is obtained by normal development and which may increase in density as the support is approached, comprises developing the latent image, without reversal, by the use of a developer containing a retarding or inhibiting substance which when in use is gradually exhausted by forming a stable complex salt or an tmdevelopable silver compound with the silver halide, or by combining with the gelatine layer or by absorption thereby, the substance being initially present in proportion such that during the penetration of the developer through the emulsion layer the retarding or inhibiting effect is reduced to such an extent that the developer becomes substantially more reactive as a developer, as it penetrates towards the support. Retarders or inhibitors specified are alkali-metal thiosulphates and ammonium thiosulphate, and soluble iodides and sulphides. Potassium metabisulphite and sodium bisulphite, which are capable of combining with the gelatine, may be used with an amidol developer. Energetic developers such as Metol with a caustic alkali, amidol or hydroquinone, are preferably used. The proportion of thiosulphate in the developer may be between 0À5 and 6 per cent and normally is less than 3 to 4 per cent by weight on a developing solution of normal concentration. Examples of developing formulae are given. The Provisional Specification refers also to the use of cyanides as inhibitors and to the development of lenticular-screen materials.