MODEL FOR THE CHEMICAL SENSITIZATION OF SILVER HALIDE PHOTOGRAPIC EMULSIONS WITH SULFUR AND GOLD.

A multistep scheme for the reactions comprising chemical sensitization of a silver halide photographic emulsion with conventional sulfur and gold reagents is proposed, based on published observations. The steps include, among others, the deposition (which may be gold catalyzed) of silver sulfide, its migration to form sulfur sensitivity specks,and the reduction of gold ions to form gold sensitivity specks. The model is tested in a series of experiments on the kinetics of chemical sensitization of a silver iodobromide emulsion which yields insignificant response to light with the developer chosen in the absence of intentional chemical sensitization. The results are largely consistent with the proposed reaction scheme, and confirm the two-step formation of sulfur sensitivity centers, with gold mediation of the initial deposition of sulfide.