Ammonium thiosulfate is a highly active chemical used as a rapid fixing agent in photographic processing. It works by converting unexposed and undeveloped silver halides in film or paper into soluble silver complexes, which can then be washed away, stabilizing the image. Because of its fast-acting properties, ammonium thiosulfate allows shorter fixing times while maintaining image quality, making it ideal for high-speed darkroom workflows. Proper use ensures clear, stable negatives and prints with minimal emulsion softening. It is commonly used in black-and-white photography, archival processing, and specialized high-efficiency developers and fixers.