Abstract: The use of a 4-thiohydantoine in combination with an image-wise exposed diffusion transfer element comprising a negative silver halide emulsion layer and an associated physical development layer containing cadmium sulfide nuclei and an associated initially immobile dye-providing substance provides improved diffusion transfer dye images.

Abstract: The use of a soluble, reducible silver salt in combination with an imagewise exposed diffusion transfer photographic element comprising a negative silver halide emulsion and an associated physical development nuclei layer provides a resultant photographic image having intensified maximum density areas with little or no effect on minimum density areas.

Abstract: Tanning (hardening) agents in a colloid layer of gelatin or the like are inactive at ordinary temperatures but are activated at temperatures above 70.degree.C. to rapidly tan the colloid in which they are incorporated. Suggested uses are in thermography and photography. Specific examples describe various gelatin layers containing the heat-activated hardeners. The class of useful tanning agents is described by the formula ##SPC1##Wherein the substituents R and R' are selected from hydrogen and halogen atoms and alkyl, carboxyl, alkoxy, formyl, tertiary amino and sulfo radicals. Some specific new compounds of this class are described.