Photosoluble Direct Positives.

The general characteristics of a new kind of silver halide photography are described. This process, called photosolubilization, involves treatment of the silver halide to greatly decrease its solubility in aqueous thiosulfate solution. Exposure to light restores the normal solubility. Processing an exposed film in thiosulfate solution dissolves exposed silver halide grains. The unexposed, less-soluble grains remain as a direct positive image. A normal photographic developer can then reduce this image to silver.