A study by M. H. Dickerson presented in Haist's book showed the threshold alkalinity for p-Aminophenol to be 9.35 (compared with 7.25 for Metol, for example), which would be fairly incompatible with fine grain development. Perhaps the general trend toward fine grain developers helps explain why p-Aminophenol was not ultimately more widely used as a developing agent.

Ian could probably comment on a note in Anchell/Troop (FDC) regarding later versions of "Agfa Rodinal" (or at least Agfa Rodinal as it existed at the time that book was written). Among other things they say it contained a restrainer and speculate this must mean p-Aminophenol was no longer the sole developing agent in the formula (presumably based on the low fog characteristic of p-Aminophenol on its own.