Patent GB-690996-A (GB)
Title: Process and photographic material for the production of coloured masks in photographic colour material
IPC: G03C7/18
Filed: 1949-10-21
Abstract: 690,996. Colour photography; masking. FARBENFABRIKEN BAYER. Oct. 21, 1949 [Oct. 22, 1948; July 2, 1949J, Nos. 27152/49 and 27153/49. Class 98 (ii). A material comprising at least one emulsion layer containing a mixture of silver salt emulsions of higher and lower light sensitivity, a colour coupler and development nuclei, is exposed to an object to affect only the higher sensitive salt, and treated in a colour developer containing no salts whose anions are the same as those of the higher sensitive silver salt, and in which developer the lower sensitive silver salt is more soluble than the higher, whereby a negative colour image is produced from the exposed silver salt of higher sensitivity and a positive colour image is produced from the non-exposed silver salt of lower sensitivity. Preferably the higher and lower sensitive silver salts are the bromide and chloride respectively, and the reaction proceeds as described in Specification 690,997 for producing positives directly. Use of other silver salts such as the oxalate, stearate and ferrocyanide is suggested. In a second form of the invention, in which form the light sensitive materials are included therein, the mixed silver salt layer with coupler and nuclei is used primarily for mask formation and a normal silver halide-coupler layer or layers are used for the images. The higher sensitive portion of the masking layer, usually silver bromide, may amount to no more than ten per cent of the sensitive mixture and may be sensitized to the same region of the spectrum as its adjacent image - forming sensitive layer. Exposure, colour development, bleaching and fixing of such material produces a negative colour image in the image layer and a positive colour image and a very weak negative colour image in the masking layer; such weak negative colour image may, however, be avoided by inclusion of a non-colour developing substance in the colour developer. In a multilayer material one or more of the masking layers may be applied as desired adjacent to, or separated by a thin gelatin layer from, the image layer or layers which are to be masked. Couplers in the masking layer and corresponding image layer may be the same or different. In a single example an otherwise conventional subtractive multilayer colour former negative has the masking layer containing a silver chloride emulsion, and a much smaller proportion of a higher sensitive silver bromide emulsion sensitized to red and green, colour formers for yellow and red, and colloidal silver, between the normal. red and green sensitive layers; after exposure this negative is treated in a colour developer. containing a little metol, and sodium sulphite as silver chloride solvent, bleached and fixed, to provide a yellow-orange mask in the masking layer. in addition to the normal partial images in the emulsion layers. Specification 634,169 also is referred to. The Specification as open to inspection under Sect. 91, suggests also a process of mask formation by dissolving silver salts not used for development of the colour images and developing these dissolved salts with the aid of development nuclei. This suggestion does not appear in the Specification as accepted.