Pyro is a chemical reducing agent occasionally used in photographic developers to convert exposed silver halides into metallic silver, forming the visible image on film or paper. It is known for producing rich, warm tones and high-contrast effects, particularly in black-and-white printing.
While less common in modern mass-market processing, pyro is valued by fine art photographers for its ability to enhance image permanence, tonal depth, and subtle gradation. Careful handling is required, as pyro solutions can be toxic and require precise mixing for consistent results.