Does anyone use a carbonate/bicarbonate buffer? The pKa for the second dissociation of the carbonic acid/bicarbonate/carbonate system is about 10.25, or maybe it's 10.23, but anyway assuming it is 10.25, an equimolar mixture of carbonate and bicarbonate should give a pH of about 10.25. I gather from discussions about pH and development that a pH of 10.25 would put a developer in the active range, but not extremely active, and the buffering capacity would be high, depending of course somewhat on the absolute concentrations. At a molar ratio of [CO3--]/[HCO3-] the pH would be about 9.25, and the buffering capacity would be moderate, again depending somewhat on the absolute concentrations. If I recall correctly, a pH of 9.25 is below the threshold of strong developer activity for ascorbate and is close the the practical threshold of moderate to strong developer activity for para aminophenol. Taking these broad concepts to a specific developer formulation concept (i.e. raising a second topic of discussion for this thread), maybe making a pH 9.25 bicarbonate/carbonate buffer with (a super additive) para aminophenol and ascorbate developer combination could be interesting. The pH might be low enough to tame ascorbate's tendency to fog film by keeping it from being he main developer, but high enough to allow the para aminophenol to be the main developer. Because the buffering capacity of this buffering system at pH 9.25 would be relatively low, the tendency for oxidation of ascorbate to lower the pH may be only partially compensated by the buffer, especially if the total buffer concentration is kept low, so there may be a moderate compensating effect and/or edge effect when using this mixture. One nice thing about this proposed system is that it would be possible to make it at home using relatively common ingredients, a desirable thing, but not necessarily the main idea of this thread. Of course, I haven't tested this. I am just throwing out this concept for discussion.