The Diffusion of Dyes in Gelatin

Abstract

The study of the diffusion of dyes through gelatin is of particular interest in connection with dye imbibition processes of colour photography. In the present work, the diffusion of a dye through, or from, a gelatin layer on film base is instantly arrested by plunging the specimen into a solid carbon dioxide-alcohol bath at -80°C. so as to freeze the contained water. It is then transferred to a drying chamber in which the Ice is volatilized from the gelatin in a current of cold, dry nitrogen. The dried sample is then cross-sectioned with a microtome and mounted, after which it is scanned with a recording high-resolution microdensitometer of new design. Densitometric curves obtained in this manner are presented and discussed. It is shown how the concentration profile of a diffused dye may change at different values of dye-bath pH, and how the presence of a mordant alters the concentration profile. It is also shown how the diffusivity and substantivity of a dye may be greatly altered by certain relatively minor changes in dye structure. Finally, the process of transfer of dye by diffusion from a matrix into a mordant blank is displayed and the role of the mordant is discussed.