Catechol Pyrocatechin, also known as Pyrocatechin and Pyrocatechol, is used as a developing agent for black and white film or paper.
It gives warm black images, with rapid development and high contrast. Pyrocatechin also acts as a tanning developer, which stains (actually fogs) the negative and also hardens the emulsion protecting it from reticulation. Pyrocatechin is easily soluble in warm water. It is chemically akin to hydroquinone but with special properties, notably the fact that it oxidizes readily and its oxidation products have a tanning effect on the gelatin. When used without sulfite, or a very low sulfite content, it gives a heavily stained image and tans the gelatin in proportion to the density of the image.