Theory and Control of Wet-to-Dry Density Changes of Photographic Aids.

Unpredictable wet-to-dry density changes in photographic films are shown to occur in two successive stages during drying, one is reversible the other irreversible. These changes in the silver image are related to changes in configuration of the gelatin molecule and are therefore very sensitive to slight variations in processing and drying conditions. Above a critical temperature, Tc, melting and reforming of gelatin crystal-lites causes a marked shift in the magnitude and direction of the density changes. By substituting for gelatin an emulsion binder which minimizes compression and orientation of the silver image the dependence of wet-to-dry density changes on processing conditions was virtually eliminated.