Hydroquinone (1,4-Dihydroxybenzene);Originally Posted by avandesande
All three of these Benzine Ring compounds have the potential to act as tanning and staining developers. Sulfites can depress or stop the tanning and staining with all three.
Pyrogallol is the most active of the three. Catechol is less active than Pyrogallol and more active than Hydroquinone. In general, it is possible to substitute one of these reagents for another, taking into account the differences in activity.
All three developers become more active in the presence of sulfite - but with addition of too much sulfite lose their ability to stain and tan.
All three developers are additive (show increased activity) or are superadditive with phenidone and phenidone derivatives.
All three developers are additive with Metol.
All three developers are additive (or superadditive) with ascorbic acid.