Some Aspects of the Desensitizing Effect of Rhodium Salts on the Photographic Emulsion

Abstract

Desensitizing effect of rhodium chloride on silver halide emulsion and its exposure intensity dependence were compared with those of rhodium nitrate and pinacryptol yellow. Rhodium chloride shows powerfull desensitizing effect at either high or low intensity exposure, but pinacryptol yellow is effective only at low intensity exposure. The similar exposure intensity dependence was observed on the solarization promoted by rhodium chloride and pinacryptol yellow. The chemically fogged emulsion containing rhodium chloride is solarized at high or low intensity exposure, however pinacryptol yellow can not promote the solarization at high intensity exposure. Rhodium nitrate gives little influence on the photographic emulsions.
For observation of the behavior of rhodium chloride in the emulsion, the contents of rhodium and X-ray diffraction of the silver chloride precipitated in presence of rhodium chloride, and polarographic reduction potential of rhodium chloride were determined. The results suggest that the desensitizing effect of rhodium chloride is due to electron trapping by rhodium ions occupying lattice points of silver halide. It may be considered that rhodium ion in silver halide more quickly captures photoelectron near the released point of electron than pina cryptol yellow adsorbed on the grain surface.