Quote Originally Posted by Photo Engineer View Post

Sulfite also drags the oxidation of HQ to the right by scavenging the quinone by generating HQ monosulfonate which itself is a weak developer.

But, as a number of people have said, the use of more than two developing agents is a real reach. I know that Haist has said that, and probably Henn and Lee as well.

BTW, I have also made mention elsewhere of ETA developers. They are distinguished from superadditive developer combinations by having the pH adjusted to be optimum for the primary developer. The primary developer is present at very low concentrations. The other developer is not really active under these conditions except to regenerate the primary developer. These are unique and AFAIK there are not currently on the market.

OK, but try the combination of Metol-hydroquinone without sulfite. How much superadditivity do you get? Now add a very small amount of ascorbate and see what happens. While the thought of a developer without sulfite is repugnant to some, it is very handy to have a sulfite-free staining developer all of whose components are soluble in glycol. Granted, HC110 solved that problem with an organic sulfite, but it is not a staining developer. Sulfite in rather small concentration prevents staining in catechol or hydroquinone developers. It takes more to eliminate staining by pyrogallol, but it can happen. If the stain is not desired, sulfite added to the working solution will prevent it, and there is a wide latitude in the measurement of its quantity.

A superadditive mixture of Metol or Phenidone with ascorbate is obtained without sulfite and is non-staining.