D-76 shadow detail

Terrance: 'Lygadol' somehow does not sound as professional as Rodinal, but what works for me is this:

Pan F+: at my 90F, I dilute 'Lygadol' 1 + 2 and develop for 7 minutes. At 75F, try doubling that time. That is why you will probably wish to NOT dilute. But, I have NEVER experienced any deleterious effects at that nice, lukewarm temp. Make CERTAIN that all subsequent solutions are also as temperate, however.

For Tri-X and the TMAX films, try doubling those times. Or, to have more manageable times, I develop Tri-X and the TMAX films at a dilution of only 1 + 1 for eight minutes, again, at 90F. So, again, either double development times for the colder, more 'normal' 75F, or do NOT dilute for yet shorter development times. - David Lyga

Michael, I am surprised that no one seems to explain why phenidone provides greater emulsion speed than metol. Based on the mechanics of super-additivity I would guess that it depends on the electron density on the nitrogen atoms of phenidone and metol. The difference in density allows phenidone to bind more strongly with activation centers in the exposed emulsion. Having done research on the strength of metal-nitrogen bonds for ammonia adsorbed on metal substrates this idea makes sense to me. Sounds like a good PhD candidate research problem.

Phenidone really doesn't have to be a good developing agent since the real work is done by the other agent in the super-additive mixture. To put it in militaristic terms think of the nitrogen containing agent as providing a "beach head" in the emulsion. Phenidone is just better at doing this than metol.

Gerald C Koch said:

Michael, I am surprised that no one seems to explain why phenidone provides greater emulsion speed than metol. Based on the mechanics of super-additivity I would guess that it depends on the electron density on the nitrogen atoms of phenidone and metol. The difference in density allows phenidone to bind more strongly with activation centers in the exposed emulsion. Having done research on the strength of metal-nitrogen bonds for ammonia adsorbed on metal substrates this idea makes sense to me. Sounds like a good PhD candidate research problem.

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Found something in Photographic Theory and Practice, LP Clerc, Vol 4 Monochrome Processing, revised by R E Jacobson 1971 p473 (extracts):

"No regeneration of phenidone occurs in a Phenidone -hydroquinone developer in the absence of sulphite (ref). Moreover the primary developing agent or its oxidation products must sulphonate less readily than the secondary developing agent or its oxidation products because otherwise the primary developing agent would be removed from the grain surface and the regeneration step would not readily occur. This condition is fulfilled by phenidone and explains in part why Phenidone-hydroquinone developers are more efficient than metol-hydroquinone developers because the oxidation product of Phenidone does not react with sulphite, whereas the oxidation product of metol can be sulphonated (ref).
A second contributing factor to the higher activity of Phenidone-hydroquinone developer than metol-hydroquinone developers is that hydroquinone monosulphonate can itself form a superadditive developer with phenidone (ref) but is not superaddditive with metol."

Alan, Thank you for this additional information. More to ponder.

Michael R 1974 said:

The problem for me is that superadditivity, Phenidone etc. are always discussed in terms of "activity" and "efficiency". None of that really addresses the sensitometric characteristics of either agent or the combination. It would be helpful to have an analysis of the developing activity of Phenidone on its own since it is quite unique. It isn't in any of the books/papers I have.

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Michael, I’m not sure if this is what you are seeking, but this is an extract from “Developing” 18th edition by K.I. Jacobson and R.E. Jacobson. 22nd reprint, page 101.

Phenidone
1-phenyl-3-pyrazolidone

When used alone in sodium carbonate-sulphite solutions, it gives very fast but extremely soft working developers.

Mick.

Mason. Photographic processing Chemistry 1975 notes that it was shown that free radicals formed in the alkaline oxidation of phenidone (no superadditive substance present) can combine to form a molecule of phenidone and an unknown compound which reacts slowly to give the pyrazolone (attachment). The pyrazolone can exist also in ionic form in alkaline solution.
From Anchell and Troop in The Film Developing Cookbook p96 "..the oxidation products of phenidone ...retard development...makes POTA such a low contrast developer."
One can guess the Pyrazolone is adsorbed on silver grains and determines the curve shape but confirmation of this is missing.

That's what I need, "retard development". Then I can understand it. Guess there's a reason phenidone is missing from my own darkroom
supplies.

I fiddled with phenidone long ago, but ever since I switched to pyro tweaks for general shooting, haven't really seem to need it. I had three
years of organic chemisty in college long ago, but find life more pleasant having forgotten all that and devolving into a simple darkroom
alchemist.

Hey Drew, Are you using Pyrocat or Pyrogallol?

Michael R 1974 said:

Anchell/Troop is the kind of thing I'm talking about - ie not specific enough to explain the curve shape relative to an aminophenol such as metol - which also has oxidation products which retard development. According to Haist, sulfite counteracts this in the case of Phenidone as it does in the case of metol.

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Are you sure Haist says that about phenidone? Mason not only wrote a book but worked and published on the subject of phenidone. From his book p84:

"Axford and Kendall showed that the pyrazolone is formed in quantitative yield when Phenidone is the sole developing agent,Axford and Kendall also showed that that no sulphonation occurs when Phenidone is oxidised in presence of sulphite.This is an important difference between Phenidone on the one hand and hydroquinone and metol on the other."

I've tinkered with all kinds of pyro formulas of both categories, but have otherwise largely standardized on pyrogallol for routine work. I get exactly what I want in terms of negative printability, so why fix something that isn't broken at this stage of the game? My fussing around with all kinds of MQ and other developers is more related to papers or specialized lab film applications, including quite a range of masking options, color separation negatives, and now experiments to revive wash-off relief color printing, which have go quite well in this respect, but shy of the sheer time commitment I need to do the logistics of printing itself, since I'm not quite retired from my day job yet. Like I said, I'm more of an alchemist, but when I do need to crunch some legit chemisty to get thru a roadblock, will do it. Too many things going on at once; that's why I keep several distinct darkroom spaces. Color gear is set up with one set of enlargers, black and white with another, plus gear to nitpicky film work per se. It's all fun, and I do appreciate some of these more technical discussions. But I am way behind the curve on the subject of phenidone.