Catechol and Superadditivity

mrred · Feb 26, 2016

ritternathan said:
These are the instructions that I followed and have used to make Pyrocat-MC at home. You can use the TEA and/or water method but it mostly defeats the purpose of using glycol in the first place. I used an old candy thermometer. Use pyrex and thick, good heat resistant gloves and do it outside if you can.

The one on the left was made with tea and the one on the right was made with glycerin, as per Pyrocat mixing instructions. The glycol started out yellow. The tea is turned the least. As you can see, the samples are not that old.

edit: This is feb 26

Gerald C Koch · Feb 26, 2016

Rudeofus said:
For some reason I don't know a single Metol based developer which is sold as a concentrate, which strikes me as odd. Does anybody here know one, even it it contains a secondary development agent or is/was sold as two part concentrate.

I have seen several formulas some under the heading of Metol Caustic. IIRC Ethol sold theirs under the name Ethol Blue. I used it many years ago. Here is my take on a formula

Distilled water 900 ml
Metol 16 g
Sodium sulfite 40 g
Sodium hydroxide 7.5 g
Water to make I l

Dilute 1+15 or 1+31. Depending on the film use times of 8 to 12 minutes @20C.

Nothing commercial now, but Metol forms a phenolate with hydroxides just like PAP does so very concentrated solutions like Rodinal are possible. At a lower concentration there is the Beutler developer. I posted a formula which uses Metol and hydroquinone under the name Kalogen. It is diluted 1+49 and produces very nice results. Also The Focal Encyclopedia Of Photography, Focal Press (London:1962) p 319 lists a highly concentrated Metol developer.

mrred · Feb 26, 2016

Gerald C Koch said:
It is seldom necessary to use more than two developing agents in the same formula. Occasionally you will see a third one like Glycin or PPD but their presence is for other purposes. Both Metol and Phenidone are super-additive with catechol so you could eliminate either one. As mentioned in my previous post, the optimal ratio effects only the rate of development but NOT is final outcome. So it is more of a theoretical consideration than a practical one. You will find ratios for the same developing agents that vary widely. Usually the bottom line is the determining factor.

The best (lasting) Catechol developer I used was Hypercat. It has never failed, but I am not satisfied with the level of stain.

When I bought Pyrocat-HD, it went dead in about 4 months. It was the water version so I took that with a grain of salt. I then made a litre of Pyrocat-MC in glycol/glycerine and it went bad within a month. Wasn't impressed with loosing 50g of catechol.

I looked at his formula closer and suspected he wasn't using an optimal ratio. I'm sure he had his reasons, but figured I'd try what I described here with the water based formula. The development was exactly what I wanted in terms of stain, activity and grain. I just could not make the stuff last. And that's why I am looking at the glycol versions.

The super-additive is exactly what I want. Otherwise I will go back to Hypercat......which never dies.

mrred · Feb 26, 2016

Rudeofus said:
Assuming you refer to part A as listed in (there was a url link here which no longer exists), there is some form of Sulfite in your mix, it's just not very much.

I have two questions:

For some reason I don't know a single Metol based developer which is sold as a concentrate, which strikes me as odd. Does anybody here know one, even it it contains a secondary development agent or is/was sold as two part concentrate ?

Your part A concentrate is not that much different from D-23 working solution with an extra 60 g/l Catechol and, of course, an acidic pH. Both the Catechol and the low pH should IMHO extend working solution shelf life of D-23, so your concentrate should last longer that the 6 months specified for D-23. Are you sure that your part A is toast after a few weeks, or does it just change color?

1: Gerry answered that one.

2: D23 has metol and Sodium Sulfite. That's it. This is a Catechol based developer. The Sodium Sulfite is the preservative that makes Metol in D23 last and cannot be used in a catachol based staining developer as it will prevent the staining. The two developers are in no way similar except they both contain Metol.

Gerald C Koch · Feb 26, 2016

The problem with many of the staining developers is that they are not really staining developers. If you want good stain then there cannot be much in the formula that will compete with the stain image. This includes too much sulfite AND developing agents that will compete with the staining developing agent but which produces no stain image. Ascorbic acid is a particularly eqrigious example of what to leave out. So it is a completion between the two type of developing agents; staining and non-staining. Finding the correct balance is the key.

Here's a catechol developer one of the German ones that I mentioned previously.

Catechol Acutance Developer

Part A

Distilled water 90 ml
Sodium sulfite 1.25 g
Catechol 8 g
Water to make 100 ml

Part B

Distilled water 100 ml
Sodium hydroxide 10 g

Part B is correct as given being a total 100 ml of concentrate.

For use take 25 ml of A, 15 ml of B, and dilute to 1 liter. Develop for 15 to 20 minutes at 20C. Discard after use.

I haven't used it but from the low sulfite concentration it should produce good staining.

mrred · Feb 26, 2016

I wonder if that little amount of sodium sulfite would be enough to preserve the Metol.

Murray Kelly · Feb 27, 2016

Gerald C Koch, post: "De mortuis nil nisi bonum "
Speak no ill of the dead.
Has Patrick died?

Wayne · Feb 27, 2016

Murray Kelly said:
Gerald C Koch, post: "De mortuis nil nisi bonum "
Speak no ill of the dead.
Has Patrick died?

Yes he passed away last year.

Rudeofus · Feb 27, 2016

mrred said:
2: D23 has metol and Sodium Sulfite. That's it. This is a Catechol based developer. The Sodium Sulfite is the preservative that makes Metol in D23 last and cannot be used in a catachol based staining developer as it will prevent the staining. The two developers are in no way similar except they both contain Metol.

Look at your formula: your concentrate contains 10 g/l Metol and 35 g/l Sodium Metabisulfite, in terms of sulfite that's about half of what you have in D-23. That's certainly not nothing. The Catechol should rather increase shelf life, not decrease it. Likewise, Metol should last longer in acidic environment.

I still wonder whether you see harmless discoloration or a real weakening of developer activity.

mrred · Feb 27, 2016

I've noticed some consistency in your postings. Is everything you see with Metol as an ingredient D23 to you? Perhaps you should discuss the merit in another thread.

Alan Johnson · Feb 27, 2016

The samples illustrated in post 26 look normal to me,
When I used to use PC-TEA it very slowly went nearly black in a nearly empty bottle over the course of a year but it still worked.

mrred · Feb 27, 2016

In this case, it's just the Metol that dies and you lose the super-additive effect. Development times get much longer.

Metol is supposed to be preserved with an acid, but it doesn't seem to work. Ian Grant had mentioned if the bisulfite was not fresh it may break down. Some of the possibilities.

The glycol based versions of Pyrocat-HD and Hypercat use ascorbic acid to expunge the oxygen, but it hasn't helped the Metol here.

But I am surprised with the tea version I made. It's an alkali with some water mixed in, and it lasts (a little) longer.

With Gerry's posting I remembered that Barry Thornton used 2g of Sodium Sulfite in his dixactol. That wasn't enough to effect the stain and it might be enough to preserve the Metol. Made a batch and is sitting on the shelf now. Time will tell.

Murray Kelly · Feb 27, 2016

Wayne said:
Yes he passed away last year.

Thank you. Sad.

mrred · Apr 21, 2016

An update: The sulfite did the job quite nicely. It's halfway through April and my batch I made in Feb (since last post) still lives and works like a charm.

The working formula is as follows.

MCAT

Part A
70 ml dist water
2g sodium sulfite
6g catechol
1g metol
top to 100 ml dist water

Part B
70 ml dist water
10g sodium hydroxide
top to 100ml dist water

I use 1:1:150 and 8 mins (rotory drum) is a good place to start. The stain (brown) is typical of this kind of developer. I see no reason why you couldn't use a carbonate alkali. Adjust your development times accordingly.

This is a cheap, easy to make, and effective pyro developer. The big advantage of using a water base (vs glycol) is the low insolence of water contamination when you clean your syringes.

Raghu Kuvempunagar · Feb 19, 2019

Gerald C Koch said:
I have seen several formulas some under the heading of Metol Caustic. IIRC Ethol sold theirs under the name Ethol Blue. I used it many years ago. Here is my take on a formula

Distilled water 900 ml
Metol 16 g
Sodium sulfite 40 g
Sodium hydroxide 7.5 g
Water to make I l

Dilute 1+15 or 1+31. Depending on the film use times of 8 to 12 minutes @20C.

Nothing commercial now, but Metol forms a phenolate with hydroxides just like PAP does so very concentrated solutions like Rodinal are possible.

Interestingly, Gainer has elsewhere (https://www.photography-forums.com/threads/rodinal-and-patrick-gainer.93741/) given a formula that is almost similar to Gerry's above formula (but four times more concentrated):
Water (125°F/52°C) 750.0 ml
Metol 63g
Sodium Sulfite 150g
Sodium Hydroxide 28g
Water to make 1l

Alan Johnson · Feb 19, 2019

Gainer had also in the recipes "Metolal" which is similar. Mine only lasted a year, not up to Rodinal standard and not cheap on metol.

Raghu Kuvempunagar · Feb 20, 2019

Alan Johnson said:
Gainer had also in the recipes "Metolal" which is similar. Mine only lasted a year, not up to Rodinal standard and not cheap on metol.

It's a bit intriguing given that your own mix of Metol, Sulphite and Hydroxide has survived for more than two years (as reported in the thread on Metol hydrolysis).

Rudeofus · Feb 20, 2019

Alan's metol hydrolysis test jumped through hoops to avoid oxygen ingres. In normal packaging his metol hydrolysis test would have oxidized.

GLS · Feb 20, 2019

Gerald C Koch said:
Simple organic compounds are usually colorless or yellow in color. An intense color often indicates that a free radical is being formed.

I would think it highly unlikely radicals are involved. There could be various reasons a coloured solution is produced; most likely from formation of a charge-transfer complex at high pH.

Pixophrenic · Feb 20, 2019

Alan Johnson said:
Gainer had also in the recipes "Metolal" which is similar. Mine only lasted a year, not up to Rodinal standard and not cheap on metol.

I am glad that this thread is apparently revived, since after my recent foray into p-aminophenol base preparation I have been itching to add to the old Gainer thread on Metolal. But, "De mortuis nil nisi bonum " has made me hesitate. Has any of your guys ever wondered why there is commercial PAP base, but no commercial metol base? I think I may have an answer: it is very unstable, much more so than the PAP base. One can, indeed, precipitate metol base, as Gainer once professed, and find that it starts oxidizing literally within minutes of preparation. It goes into glycol almost instantly, but starts oxidizing there, too, within hours. It does not keep even under a layer of sulfite solution, as PAP base does. In fact, this is the first time I have seen any developing agent oxidize in glycol so quickly. So, preparation of "metolal" is in fact even trickier than that of "true Rodinal".

As an exercise, I succeeded in preparation of modified metolal (or rather modified "Kalogen") which contains a little hydroquinone, by carefully adding alkali dropwise to metol-HQ-sulfite solution, as outlined in Koch's Kalogen, to watch the crystalline pellet that forms to go in solution. I think the secret in the keeping of certain phenolates is that they should be carefully titrated with just enough alkali to dissolve the base, and then, in the case of metol, kept in small vessels absolutely free of air. That said, the amount of alkali should be carefully adjusted, and in the original Gainer recipe there was way too much of it. User Relayer pointed to this issue but the thread died after that. On a side note, as I said elsewhere, certain brands of sodium sulfite contain quite a bit of carbonate, so that the solution's pH can be as high as 10.4. This will certainly affect the stability of catechol stocks. The Jarai metol-phosphate developer that I posted in the resource section some time ago offers a much easier access to a high pH acutance developer than does metolal, especially if metol is kept separately in a weak bisulfite solution.

Alan Johnson · Feb 20, 2019

https://www.photrio.com/forum/resources/kodak-high-definition-developer.178/
Another developer of this metol containing type.
The Film Developing Cookbook 1998 p56 notes that it was discontinued in the early 1960s with the claim that it no longer gave optimum performance with Kodak films [did they start putting iodide in them?], whilst others thought that poor shelf life was the real culprit.
Considering that many manufacturers had a Rodinal type developer, but there were no copies of single solution HDD, the latter explanation seems more likely.
Its not clear why metol oxidizes more readily than p-aminophenol when in developer solution.

Pixophrenic · Feb 20, 2019

IMHO, higher stability of metol over p-aminophenol developers could be an illusion. Partly this happens because metol developers were traditionally formulated with 30-50+ g/L sodium sulfite, while that much sulfite is detrimental to the activity of PAP, so those are usually 25 g/L and lower, if diluted. Second, PAP precipitates out of solution at pH 10.5 or lower, and is slower working overall, so PAP developers were traditionally highly alkaline, although not necessarily as high as Rodinal (12.3). Metol, by comparison, is in solution and very active at 8.0 and above, but used at the same pH as PAP it appears more prone to oxidation. In the 1920s, when transition from PAP-Q to MQ developers occurred, it also had something to do with actual purity of available chemicals. The booklet "Modern Photographic Developers" of 1918 paints a very interesting picture, where users were overwhelmed with commercial preparations of PAP and its salts under a variety of fancy names, while the author admits that products like "German metol" would be much more desirable, but unavailable at the time.

Raghu Kuvempunagar · Feb 20, 2019

IIRC Gerry's hypotheses was that Metol and Hydroquinone would form phenolates when treated with Sodium Hydroxide and the phenolates would be less prone to oxidation. His Kalogen concentrate which contained both Metol and Hydroquinone survived for several years without getting oxidised. On the other hand Metolal which contains Metol but no Hydroquinone doesn't last as long. Is Kalogen's resistance to oxidation due to the fact that it contains Hydroquinone? Is the phenolate formed by Hydroquinone somehow preventing Metol (or its phenolate) from getting oxidised in Kalogen concentrate?

Alan Johnson · Feb 20, 2019

Pixophrenic said:
IMHO, higher stability of metol over p-aminophenol developers could be an illusion,,,,,,,,, but used at the same pH as PAP it appears more prone to oxidation..

The claim is that p-aminophenol is more resistant to oxidation than metol, not the other way round.
Can a link be provided to the quoted Modern Photographic developers 1918 ?
p-aminophenol can be used to make a clone of D-76 (metol only version). it is quite stable at pH ~8.5 but takes about twice as long to develop film.

Pixophrenic · Feb 20, 2019

Raghu Kuvempunagar said:
IIRC Gerry's hypotheses was that Metol and Hydroquinone would form phenolates when treated with Sodium Hydroxide and the phenolates would be less prone to oxidation. His Kalogen concentrate which contained both Metol and Hydroquinone survived for several years without getting oxidised. On the other hand Metolal which contains Metol but no Hydroquinone doesn't last as long. Is Kalogen's resistance to oxidation due to the fact that it contains Hydroquinone? Is the phenolate formed by Hydroquinone somehow preventing Metol (or its phenolate) from getting oxidised in Kalogen concentrate?

According to Mason (p.79) "most of the metol which is oxidized by development is reduced back to Metol again by the hydroquinone even in the presence of a large concentration of sulfite". IMO, if it happens in development, what prevents it from also happening during storage? Thus even a small amount of hydroquinone added to a metol-only developer should prolong its storage life. My Kalogen is over a year old and looks pretty much the same, but its low hydroquinone "clone" is just starting, so no opinion yet.

Catechol and Superadditivity

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