What is the difference between pyrocatechol and pyrogallol, for 'simple' film developer?

Philippe-Georges · Jan 22, 2023

My basic question is what the title says.

C6H4(OH)2 <—> C6H3(OH)3

And is it interchangeable?
When a formula demands pyrogallol and I only have pyrocatechol, how to sublimate?
Examples:
- Cat-P-TEA formula
Triethalomine 100 ml
Phenidone O,2 g
Pyrocatechol 10 g => I have

- P-TEA (à la P. Gainer)
Triethalomine 100 ml
Pyrogallol 7 g (10 g à la S. King) => I don't have

koraks · Jan 22, 2023

Hydroquinone: C6H4(OH)2
And yet, it isn't the same as pyrocatechol, even though the formula looks identical.

So be careful trying to substitute one for another - they're just different compounds with different properties. Can they be substituted? Yes, but the developer won't work the same way. For instance, I've done quite some testing in getting a hydroquinone staining developer to work, and while it does stain, it never stains as well as e.g. pyrocatechol.

I'm sure some of our resident chemists can say one or two things about the relative activity (at a certain pH) of the compounds you're planning to toy around with.

From a practical viewpoint, I'd consider just digging up an attractive formula for the stuff you've got and call it a day.

relistan · Jan 22, 2023

They are not interchangeable exactly. This is a good explanation https://www.photrio.com/forum/threads/pyrochatechin-vs-pyrogallol-comparisons.8879/#post-119110

However, that second formula without the phenidone should work. But it will be a different developer, and slower. The first uses phenidone and catechol which I believe to be a superadditive pair, and would thus be faster than the formula would be without the phenidone. I have no idea what effect that has on the stain.

@Alan Johnson recently did an experiment with catechol alone at near this pH and posted this image (the center) https://www.photrio.com/forum/attachments/catechol-and-ascorbate-jpg.325991/

He might be able to tell you more.

Alan Johnson · Jan 22, 2023

Both Pyrogallol and Pyrocatechol are used as secondary developing agents to regenerate phenidone or metol. At the same time they tan the emulsion making it hard, slowing development in the highlights ,extending the tonal range. Also the sideways diffusion of developer is reduced ,increasing sharpness.

Gordon Hutchings created PMK pyro using Pyrogallol, it works at metaborate pH.
Jay DeFehr created 510 Pyro where the Pyrogallol is regenerated by ascorbate.
Sandy King found that PMK pyro oxidized in rotary processors and created the Pyrocat HD series of developers that work at the higher carbonate pH by a similar action [Borates form complexes with Pyrocatechol and cannot be used]
Jay DeFehr created Hypercat using Pyrocatechol.

These are probably the four on which most work has been done IMO.

Philippe-Georges · Jan 25, 2023

Tom Hoskins wrote (what I read via the link by Relistan):

"...In terms of activity:

Pyrogallol is the most active (arbitrary scale 100%).
Pyrocatechol is the next most active (relative scale 70% Pyrogallol).
Hydroquinone is the least active of the three (relative scale 50% Pyrogallol).

I personally favor the Pyrocatechol based developers..."

So, if I increase the amount of Pyrocatechol with 30%, would I reach the activity of Pyrogallol?

relistan · Jan 25, 2023

Philippe-Georges said:
Tom Hoskins wrote (what I read via the link by Relistan):

"...In terms of activity:

Pyrogallol is the most active (arbitrary scale 100%).
Pyrocatechol is the next most active (relative scale 70% Pyrogallol).
Hydroquinone is the least active of the three (relative scale 50% Pyrogallol).

I personally favor the Pyrocatechol based developers..."

So, if I increase the amount of Pyrocatechol with 30%, would I reach the activity of Pyrogallol?

I’d suggest using a formula that you have the chemicals for. The answer to your question is “maybe”. Depends on if you are using a superadditive mix or not, possibly pH needs to be adjusted, etc. But, if you are up for experimenting and maybe getting it wrong a few times, give it a shot and let us know.

Ian Grant · Jan 25, 2023

I'd suggest not using TEA in the first place. It's a stick mess until warmed up, not very convenient. Two Part is quick and convenient

Then I'd throw in that on its own Pyrocatechin gives fine grain, Pyrogallol doesn't, Hydroquinone can but is less active than Pyrocatechin on its own.

Ian

Philippe-Georges · Jan 25, 2023

Dear Relistan,

What I have standing in my darkroom's cupboard is:
TEA: +/-900cc (I had forgotten that bottle...).
Pyrocatechol: +/- 100g
Phenidone: 2x10g (fresh)
Vit-C: +/- ½ kg
K Br: +/- 250g
Glycerine EF3 97%: easy to get.

BTW, I have tried FX-55 but it lacks the 'punch' I am used to get from D-76 and X-Tol, and the Pyro-HD I have used for years all the sudden lost that 'punch' too, even mixed with fresh chemicals.
What I mean by 'punch' is a nice density, full box speed, not to steep tonality, acceptable (honest-) grain and somewhat open shadows.
Perhaps it has to do with my transition from Tri-X to HP5+, as Tri-X is really getting a little to pricy...

I will not buy ready made developers till that cupboard is cleaned up (I am retired now)...

DREW WILEY · Jan 25, 2023

There are so many varieties, based on both pyrocat and pyrogallol, that I don't think anyone could cite them all. I've even development a couple unique tweaks myself, which I only used once or twice myself, but did their expected job well. I do tray development of sheet film, and gentle inversion of hand drums for roll film (gave up rotary development of film long ago), so PMK pyro is my go-to staining developer. The effect of Pyrocat HD is similar, but certainly not identical; and the two are obviously based on two entirely different kinds of "pyro".

PMK is sheer magic with HP5; but I also prefer it for FP4, Delta 100, TMY400, Acros, Pan F, pretty much every sheet and roll film with respect to general photography. I do keep several other developers on hand for special applications, and now prefer Perceptol 1:3 for TMX100.

relistan · Jan 25, 2023

Philippe-Georges said:
Dear Relistan,

What I have standing in my darkroom's cupboard is:
TEA: +/-900cc (I had forgotten that bottle...).
Pyrocatechol: +/- 100g
Phenidone: 2x10g (fresh)
Vit-C: +/- ½ kg
K Br: +/- 250g
Glycerine EF3 97%: easy to get.

BTW, I have tried FX-55 but it lacks the 'punch' I am used to get from D-76 and X-Tol, and the Pyro-HD I have used for years all the sudden lost that 'punch' too, even mixed with fresh chemicals.
What I mean by 'punch' is a nice density, full box speed, not to steep tonality, acceptable (honest-) grain and somewhat open shadows.
Perhaps it has to do with my transition from Tri-X to HP5+, as Tri-X is really getting a little to pricy...

I will not buy ready made developers till that cupboard is cleaned up (I am retired now)...

You might try the formulation on this page for Instant Mytol:

Easy Film Developers – photosensitive.ca

I have not used it but have heard good things. You will need metaborate.

john_s · Jan 25, 2023

Philippe-Georges said:
Dear Relistan,

What I have standing in my darkroom's cupboard is:
TEA: +/-900cc (I had forgotten that bottle...).
Pyrocatechol: +/- 100g
Phenidone: 2x10g (fresh)
Vit-C: +/- ½ kg
K Br: +/- 250g
Glycerine EF3 97%: easy to get.

BTW, I have tried FX-55 but it lacks the 'punch' I am used to get from D-76 and X-Tol, and the Pyro-HD I have used for years all the sudden lost that 'punch' too, even mixed with fresh chemicals.
What I mean by 'punch' is a nice density, full box speed, not to steep tonality, acceptable (honest-) grain and somewhat open shadows.
Perhaps it has to do with my transition from Tri-X to HP5+, as Tri-X is really getting a little to pricy...

I will not buy ready made developers till that cupboard is cleaned up (I am retired now)...

It seems that your problem is caused by your change from Tri-X to HP5+. I am also one who has standardized on HP5+ for several reasons.

Maybe your dev procedure for Tri-X isn't optimal for HP5+ so perhaps some testing is in order. All of the developers you mentioned should give you fully developed negatives (or even overdeveloped negatives if you like).

Philippe-Georges · Jan 26, 2023

john_s said:
It seems that your problem is caused by your change from Tri-X to HP5+. I am also one who has standardized on HP5+ for several reasons.

Maybe your dev procedure for Tri-X isn't optimal for HP5+ so perhaps some testing is in order. All of the developers you mentioned should give you fully developed negatives (or even overdeveloped negatives if you like).

I an afraid that you are right, I stil have some work to do...

Philippe-Georges · Jan 26, 2023

relistan said:
You might try the formulation on this page for Instant Mytol:

Easy Film Developers – photosensitive.ca

I have not used it but have heard good things. You will need metaborate.

Thank you, it's an interesting link!

Philippe-Georges · Jan 26, 2023

DREW WILEY said:
There are so many varieties, based on both pyrocat and pyrogallol, that I don't think anyone could cite them all. I've even development a couple unique tweaks myself, which I only used once or twice myself, but did their expected job well. I do tray development of sheet film, and gentle inversion of hand drums for roll film (gave up rotary development of film long ago), so PMK pyro is my go-to staining developer. The effect of Pyrocat HD is similar, but certainly not identical; and the two are obviously based on two entirely different kinds of "pyro".

PMK is sheer magic with HP5; but I also prefer it for FP4, Delta 100, TMY400, Acros, Pan F, pretty much every sheet and roll film with respect to general photography. I do keep several other developers on hand for special applications, and now prefer Perceptol 1:3 for TMX100.

When searching for PMK's formula, I encountered some differences, what is the right one now?

DREW WILEY · Jan 26, 2023

For tray or hand-inversion drum usage, simply go with the original Gordon Hutchings version of PMK . You can get A&B liquid concentrate kits from Photog Formulary, sparing you from dealing with pyro powder. I don't recommend it for high RPM roatary drums, even modified version. Certain pyrocat formulas can do a better job of that without over-oxidizing. But I prefer PMK's handling of grain structure in most instances. I always wear nitrile gloves for any kind of darkroom chem, but it's especially important with pyro to keep it from skin or eye contact.

What is the difference between pyrocatechol and pyrogallol, for 'simple' film developer?

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