One speculation.(posted 8355 days ago)Superadditive effect of PQ is very strong and I feel PQ developers must be very carefully designed to tame this wild combination. One problem I had with PQ formulae that I thought were not well optimized was gradation that wasn't clean and beautiful. One way to tame this could be to buffer the developer, and this could lead to lack of subjective sense of sharpness. Phenidone-ascorbic acid superadditivity seems to be much easier to control and they also seem to result in noticeably finer grain than PQ. In this sense I think hydroquinone and ascorbic acid are very different.
Some people are crazy about phenidone-glycin type developers and I hope those people can describe why they love those compared to MQ, PQ and P-V.C. types.