Potassium sulfite for extreme pushing?

Anchell and Troop, in the Film Developing Cookbook 2nd ed. (p. 122), recommend Ilford DDX as the best developer for extreme pushing. I assume that extreme pushing means a two-stop or more push. Based on French research, they theorize the use of potassium sulfite instead of sodium sulfite in DDX may increase film sensitivity. It may be worthwhile, they suggest, to experiment with using potassium sulfite in other developers such as Xtol. Potassium sulfite has the disadvantage of being more expensive than sodium sulfite and accelerating the exhaustion of fixers.

Whatever you try, a simple test is all that's needed. It's possible that simply adding extra sodium sulfite would have the same effect.

There are lots of ways to increase apparent ISO, some easier than others, and most can be used in combination -- but simple testing is necessary.

bluechromis said:

they theorize the use of potassium sulfite instead of sodium sulfite in DDX may increase film sensitivity

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Hmmmm. Very skeptical about this, to begin with. But OK.

However, this here is really doubtful:

bluechromis said:

experiment with using potassium sulfite in other developers such as Xtol

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XTOL contains a pretty massive amount of sodium sulfite. If you add a little potassium sulfite to it, there'll still be a mass of sodium ions swimming around in the final soup. I doubt that the potassium ions are going to be doing much good, at all. They likely won't make any difference at all.

What you might try if you buy into the whole 'K+ will increase film speed' hypothesis, is brew an XTOL clone using potassium sulfite instead of sodium sulfite. That way, you'll only have some sodium present from the metaborate, and if you're feeling particularly feisty, you might replace the small amount of sodium carbonate with potassium carbonate for good measure. Test this mixture back-to-back with the same formula with sodium ions and see what you get.

I don't think there's going to be a difference, so I personally won't spend time testing it. But if you do, I'm sure many of us would be very interested to hear the results.

Think about it - if raising film speed in a meaningful way would have been as easy as replacing some sodium salts with the potassium species, we would see the latter being used in virtually all developers, since they would outperform the 'old-fashioned' sodium-chemistry based soups. Case in point: official XTOL! However, having looked at many developer formulas, I only see the potassium species being used if solubility is a concern.

In all my experimentation with pushing film with a low light source I have only been able to get about a quarter to a third of a stop beyond two stops with the array of standard developers. These times for squeezing ISO 3200, 6400 out of 400 film or 12,500, 25,000 out of a 3200 film is bogus in my opinion. I can't say what the effective ISO is but if you want to go really higher than you should try something like D19 or Dektol* as a developer. That seems to really max out film speed and may not be as grainy as one would expect depending on the film. Also, I came across a varion of D19: D19 Plus which adds 1.5 grams of phenidone per liter for added speed. It might be worth experimenting with just adding phenidone to any developer for added speed.

* Dektol (or similar print developer) initial 1 gal. stock solution diluted 2parts with 1 part water has the same amount of developing agents as D19. It produces slightly more speed and grain than D19 on some films.

bluechromis said:

Anchell and Troop, in the Film Developing Cookbook 2nd ed. (p. 122), recommend Ilford DDX as the best developer for extreme pushing.

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To be fair, exact quote is: "For extreme pushing we recommend Ilford HP5+ at EI 2400 or 3200, processed in Ilford DDX 1+4 for 18 minutes at 75F."

The precision is important for the discussion, as not everybody has the same definition of "extreme pushing".

They suggest HP5+ after a short discussion about the post-2007 version of Tri-X having a poorer performance when pushed beyond 800 as the older version, and about T-grain filmed being better suited for pulling than pushing.

Also note that nowhere do they say "best." Only "recommend," and that they find DD-X is superior to D-76 for extreme pushing (their emphasis).

They also suggest two non-commercial (or no longer commercialized) developers for speed increasing, Acuspeed (FX 20) and Perfection XR-1, for which the formulas are given.

Alex Benjamin said:

To be fair, exact quote is: "For extreme pushing we recommend Ilford HP5+ at EI 2400 or 3200, processed in Ilford DDX 1+4 for 18 minutes at 75F."

The precision is important for the discussion, as not everybody has the same definition of "extreme pushing".

They suggest HP5+ after a short discussion about the post-2007 version of Tri-X having a poorer performance when pushed beyond 800 as the older version, and about T-grain filmed being better suited for pulling than pushing.

Also note that nowhere do they say "best." Only "recommend," and that they find DD-X is superior to D-76 for extreme pushing (their emphasis).

They also suggest two non-commercial (or no longer commercialized) developers for speed increasing, Acuspeed (FX 20) and Perfection XR-1, for which the formulas are given.

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Anchell and Troop say that, D-76 was "once considered to be the best developer for pushing." Then they say, "I was baffled by how DD-X could, chemically speaking, be a discernibly superior pushing developer to D-76." They also have a heading that says "Why does DD-X work better for extreme pushing?" If they are claiming that DD-X works better than what had been seen as the best, is that not tantamount to saying DD-X is the best for extreme pushing?

It was Glafkides who theorised that potassium ions are more active, Bill Troop got it from him, see p63, "Potassium Salts"

It's not theory. There are lots of formulas where you can substitute potassium for sodium & vice versa. That's why I suggested in Post #2 to just use more sodium as a cheaper alternative to switching to potassium.

I believe the theory part of it is related to the question whether developers made with potassium rather than sodium may provide a slight increase in effective film speed. The question is discussed in some detail on p 122-124 of The Film Developing Cookbook 2020.

Fully hydrated potassium ions are in fact smaller than fully hydrated sodium ions, therefore it is quite possible, that a developer having mostly potassium cations is more active than a mostly sodium cation based developer.

We need to also be aware, that Bill used to be quite skeptical of "newfangled stuff" like Citric Acid based stop bathes, newer fixer formulas or Phenidone. Seeing, that DD-X (a PQ based dev) did so much better than D-76 (MQ dev) may have sent him on a search for an explanation, and the potassium theory may have come handy. It may well explain a small fraction of the performance improvement, but certainly not the whole story.

Kodak uses sodium and potassium interchangeably in their most advanced devs (C-41 CD, E6 FD, TMAX: potassium, ECN-2, XTol: sodium), so at least Kodak probably didn't see much of a performance difference as long as the developer was set up right. @koraks probably had it right: use potassium sulfite for solubility reasons, but not in expectation of a miracle.