Pyro is a term that usually means pyrogallol, or 1,2,3 trihydroxybenzene, which is usually a staining developer and just about always a tanning developer that makes the image stand out in relief in the emulsion. Pyrocat is short for Pyrocatechin or pyrocatechol or catechol or 1,2 dihydroxybenzene, also a staining and tanning developing agent. Whether you get staining depends a lot on how much sulfite is in the developer. Less sulfite = more staining.
Originally Posted by superloaf