Response to Phenidone vs. Metol--grain

I think Ryuji has hit the nail on the head. Sharpness in development refers to adjacency effects. Adjacency effects rely upon a controlled decomposition of the developing agent. PQ combinations are more superadditive than MQ combinations. Since Phenidone is so effectively regenrated by Hydroquinone, the exhaustion rate is vastly lower, which probably accounts for the proposed lower sharpness i.e., no local exhaustion takes place. The trouble is phenidone on its own as the sole developing agent is problematic. It doesn't keep very well and produces very low contrast - POTA, a developer to provide pictorial gradation from document film, is a phenidone only developer that takes advantage of this property but otherwise for normal film, phenidone only developers are typically unusable. An advantage phenidone does provide is that it is said to provide a genuine speed increase of about half a stop (this parallels my experience). I've used a fair bit of Mytol, a phenidone - ascorbic acid developer. There is an increase in speed and apparent sharpness over other solvent developers like D23 but I haven't seen the adjacency effects provided by an adjacency developer like Rodinal or FX2 (but keep in mind that this is my subjective opinion). Single developing agent formulae are the ones that give us a good idea about individual developing agents. Once you start combining developing agents, the interactions between them can provide very different effects from the individual agents themselves. Cheers, DJ.

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