The chemical Pyrogallol is an active agent in Pyro film developers.
At one time, Pyro was a universally used developer. It was even available in prepackaged formulas from companies such as Eastman Kodak. Unfortunately, it has been almost entirely replaced by metol-hydroquinone and Phenidone-hydroquinone type developers.
The main reasons for that are the fact that Pyro stains, it must be handled carefully, and it does not keep well in solution.
When used correctly, Pyro creates a stained image of unprecedented tonal scale, especially in high values.
In combination with either metol or Phenidone, it exhibits super-additive characteristics. It produces an overall stain on the negative, which adds to the contrast of the silver image. The stain is a desirable part of a properly developed Pyro image.
Pyro tends to oxidize very rapidly in solution and cannot be kept without the aid of preservatives such as sulfuric or other acids, sulfites. Etc. Pyro should be added after these preservatives have been mixed with water.
Pyro oxidation products act as strong anti-fogging agents.
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