ИСТИНА

According to the thermodynamic theory of photographic sensitivity, all the three main stages of photographic process are stages of reduction of emulsion crystals resulting in formation of metallic silver phase. Thermal processing of the emulsion at the stage of its chemical sensitization aid the process of partial reduction of AgHal microcrystals. The process can be represented as follows: noRed- + noAg+ ↔ n1Ag1 ↔ n2Ag2 ↔ n3Ag3 ↔ ... ↔ niAgi It is accompanied by gradual accumulation of molecular silver, localized upon the internal and external surfaces of AgHal microcrystals, and by growth of the effective oversaturation and emulsion sensitivity. The value of oversaturation with free silver is unambiguously determined by the overpotential value with respect to the potential of a massive silver electrode, reached during sensitization. Redox buffer solutions, depending on the value of the created overpotential, are capable of influencing the degree of oversaturation and, therefore, the sensitivity as well. The form of the sensitivity vs. overpotential dependence is determined by the mechanism of latent image formation. We consider here two variants: the first when the latent image centres formation follows the mechanism of the photoinduced formation of nuclei and the second - the mechanism of the spontaneous formation of nuclei.