The superadditive behavior of ascorbic acid with phenidone , Metol, p-aminophenol and perhaps others is a bit mysterious to me. Hydroquinone seems to require sulfite to achieve similar synergism, while ascorbate does not. It is said the ascorbic acid is a surface developer and that the function of sulfite is to break the surface barrier. I have found that a small amount of ascorbic acid in, say, a Metol-hydroquinone solution seems to be capable of at least as much superadditivity as the MQ solution with sulfite. It will be a staining developer if used without sulfite, as would the combination of Metol-pyrogallol-ascorbate or Metol-catechol-ascorbate, or p-aminophenol-catechol-ascorbate. I only know these things from experiment. If the ascorbic is more an antiozidant than a developer in these combinations, thus literally taking the place of sulfite, I do not know. It does work, as anyone who has used Pyrocat MC can attest.