I've been toying with the idea of a Phenidone-C divided developer akin to divided D-76 or Diafine. Based on my experience with Phenidone-C so far, I propose the following formula:
Ascorbic Acid - 80g
Sodium Bicarbonate - 60g
Water - 750mL (make sure all is dissolved and effervescence stops)
Phenidone - 1g
Water to make 1L
Sodium Hydroxide - 1.45g
Borax - 6.92g
Water to make 1L
Agitate for 5 mins in part A then 5 mins in part B.
I did a quick test with the recipe scaled down to 100mL and use film clips to get an indication of activity. What I expected to happen and what actually happened really surprised me. I expected there to be no visible evidence of development in part A while the ascorbate + phenidone soaked into the emulsion and expected all the development to be visible when in part B. To my surprise, after about 1 min in part A I noticed a slight darkening of the film and after two mins it was nearly black. I thought I was going nuts here as everything I read and experienced showed that you need a higher pH to get decent activity out of Phenidone-C. The time in part A is within range of a normal 8-10 min developer. I thought I may have contaminated part A and increased the pH so I checked it with a calibrated meter and it showed 7.2 ... about what I expected being near neutral. Now this is confusing ... ascorbate developing at a pH of 7.2? I still don't believe it but I ran the same test 3 times with the same result. I have no idea what's going on here and cannot explain it. On the plus side I'm thinking with the really low pH this very concentrated phenidone-c-bicarbonate mix could be an extremely fine grained re-usable developer.
On one hand this really complicates my idea for a two part phenidone-c developer but on the other hand I may have stumbled across a new unexpected developer.
Next step is to actually process film instead of test clips to see real world results. I propose two initial tests, one with just part A for 8 mins and one with part A for 2 mins and part B for 6 mins.