GB486107A - Improvements relating to colour-photography - Google Patents

Abstract

486,107. Colour photography; stripping films. WEBB, K. W. C., and GALL, R. L. B. Sept. 28, 1936, Nos. 26199/36 and 16607/37. [Class 98 (ii)] Superimposed silver images in multi-layer photographic material are isolated by transfer from the material to a metal plate in the form of a metallic image and thence to a transparent support. In one example, a multi-layer film comprises three layers sensitive to blue, green, and red respectively, separated by inactive layers and mounted upon a celluloid support. After exposure, developing and fixing, the whole film may be hardened bv immersion for 15-20 minutes in a 5 per cent solution of alum. The first layer is then bleached as with ferric chloride, the bleaching being arrested by a weak solution of sodium carbonate. After rinsing the film is immersed in a deposition agent, e.g. 20 per cent solution of sodium chloride, potassium chloride or sodium sulphite. The first layer is then pressed into contact with a clean copper plate for 7-10 minutes. The silver chloride is converted to silver which adheres to the copper plate as a deposit. The copper plate is then made the anode of an electrolytic cell containing, for example, copper sulphate or sulphuric acid or both. Upon the passage of a small current, the silver deposit is loosened, and it is then transferred to a film of dry hardened gelatine mounted on a sheet of celluloid. The plate which has had weak hydrochloric acid poured over it, is lightly pressed onto the gelatine and the silver deposit adheres to the gelatine. The gelatine remaining in the first yellow printing layer is removed by gentle .friction and stripping, the intermediate film accompanying it. The procedure is then repeated for the second and third separation negatives. The multilayer film may comprise two outside support lavers of celluloid, and in this case, one sensitive layer and the support are stripped off before the other layers are developed and fixed and the middle layer image isolated by the transfer method described. In another modification, a layer of waterproof varnish is mounted between the blue sensitive and green sensitive layers. Upon developing and fixing, a negative image is formed in the first layer only. This image is transferred to a transparent carrier as described above, the gelatine removed by scrubbing, and the varnish layer dissolved off. After redeveloping and fixing, the remaining negative images are transferred. A varnish layer may be substituted for the inactive layer between the greensensitive and red-sensitive layers. The inactive layers may be of gelatin which melt or dissolve in water at different temperatures, e.g. at 80-90‹ F. and 115‹ F. Upon immersion at these temperatures the layers can be separately stripped. Specification 440,736 is referred to.