PROCESS AND ELEMENTS FOR FORMING DIRECT POSITIVE IMAGES

1372204 Photographic material and process EASTMAN KODAK CO 25 Nov 1971 [25 Nov 1970] 54744/71 Heading G2C Positive photographic images are prepared by (1) imagewise exposing (a) a silver iodide or iodohalide emulsion layer, (2) developing the layer to form a negative silver image and a corresponding distribution of dissolved iodide ions, (3) transferring by diffusion this distribution to (b) a silver halide emulsion layer in which the grains have adsorbed thereon an agent which retards their dissolution in a fixing solution but of which the retarding effect is reduced by iodide ions, and (4) treating layer (b) with a fixing solution to preferentially dissolve those parts of the layer to which iodide ions have been transferred to produce a positive silver halide image. The negative silver image may be fixed and/or the silver halide image converted to (i) a silver image by exposure and development or (ii) a negative dye image by the silver dye bleach process, layer (b) containing the bleachable dye. Layers (a) and (b) are preferably surface and internal latent image type emulsions respectively and may be coated on separate supports and contacted after imagewise exposure (1), or may be coated on the same support, layer (a) being removed before step (4). Preferably the solubility of the grains in layer (b) is retarded by 0.05-5g. per mole of Ag halide of heterocyclic N compound containing a mercapto group (which may be salt or tautomeric thione form) in the position alpha to N atom in the heterocyclic ring; in the Examples 1-(3-capramido)-phenyl- 5-mercaptotetrazole is used but other suitable compounds are listed.