Metol, hydrolysis

Alan Johnson · May 26, 2019

After 3 years there is no significant change in the appearance of the fully closed bottle (pic).
However on their websites:
Kodak say that D-78 in full tightly closed bottles lasts for 6 months
Ilford say that Perceptol and ID -11 in fully capped containers should last for up to 6 months.
This seems to me to imply some kind of chemical change, possibly hydrolysis, occurs in these proprietary developers.
I will let the test run on.

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Alan Johnson · May 31, 2020

After 4 years there is no visible change. Maybe next year I will test the activity of the contents of this bottle vs a freshly made up solution given in post 1 and pictured in post 20.
If there has been no change I will suggest that the reaction supporting the decomposition of metol is supported by trace metal ions, of which there were none.
This might explain why there are some reports of metol based developers lasting for years but the manufacturers give a full sealed bottle expiry date of 6 months -trace metal ions.

Alan Johnson · Apr 29, 2021

This test was concluded after very nearly 5 years.
The color of the developer in the sealed bottle remained virtually the same (pic)
A test film was developed for the same time (20min 20C) in a sample from the sealed bottle and in fresh developer prepared to the same formula (post 1).
There was no visibly detectable difference in density between results from developer aged 5 years and fresh developer (pic).
Conclusion- metol was not significantly hydrolysed after 5 years at this solution pH.The test does not detect very small changes.

A sample of the same solution formula (post 1) in a 100ml sealed bottle with a plastic cap went a brown ale color after being sealed for 5 years.
This may at least partly explain why the shelf life in sealed bottles is often quoted as 6 months as they are generally supplied or kept in plastic bottles.
A deposit of 0.1g of beige colored substance was found in this bottle. It was not metol as it showed no developing activity in sulfite-hydroxide solution.
It might have been an oxidation product.

Donald Qualls · Apr 29, 2021

So it seems a reasonable conclusion after all this time is that if our developers don't last it's because our storage vessels are permeable (presumably to oxygen).

Tempting to suggest running another test (perhaps not a full five years) with a plastic capped bottle, but the solution inside blanketed with argon or butane (heavier than air, oxygen free).

Alan Johnson · Apr 29, 2021

Another thing from the test just concluded, I did notice that when I removed the stopper from the bottle containing the yellow solution, and left it off for an hour or so, the solution quickly turned to brown ale color. I don't recall unstoppered Rodinal or Parodinal bottles changing to a darker color so rapidly. Maybe this is why a metol version of Rodinal is not sold, short shelf life.

Donald Qualls · Apr 29, 2021

Alan Johnson said:
the solution quickly turned to brown ale color.

Metol in solution without preservative will go off in minutes. With preservative, it should last about as well as stock developer solution (D-23, for instance, that's just metol and sulfite).

On the other hand, p-aminophenol starts to oxidize pretty quickly too, if you don't add the sulfite right away -- I've seen Parodinal turn pink almost instantly after adding the acetaminophen to the sodium hydroxide solution -- if I add (some of) the sulfite first, I have to wait days for that pink that indicates the developer is ripe enough to use.

Rudeofus · Apr 29, 2021

Alan Johnson said:
I don't recall unstoppered Rodinal or Parodinal bottles changing to a darker color so rapidly. Maybe this is why a metol version of Rodinal is not sold, short shelf life.

Let's not forget, that Rodinal is an extremely concentrated liquid, which means it can not dissolve much Oxygen. You may get similar results with Metol in saturated K2CO3 solution.

Donald Qualls · Apr 29, 2021

Rudeofus said:
Let's not forget, that Rodinal is an extremely concentrated liquid, which means it can not dissolve much Oxygen. You may get similar results with Metol in saturated K2CO3 solution.

Well, Rodinal also contains 50 g/L of sulfite; in concentrate. DK-25 is porbably close to that than Metal in potassium carbonate solution.

relistan · Apr 29, 2021

Very interesting result, @Alan Johnson . I may need to invest in some glass...

john_s · Apr 29, 2021

I stopped using glass stoppered bottles for long storage when they became very difficult to open (alkaline solutions dissolve glass a tiny bit). Now I use Schott glass lab bottles, with blue plastic screw caps. I've wondered if they are a very superior plastic (they are a bit expensive) and consequently better for long term storage than most other plastics?

GLS · Apr 30, 2021

john_s said:
I stopped using glass stoppered bottles for long storage when they became very difficult to open (alkaline solutions dissolve glass a tiny bit)

It isn't because they dissolve the glass (that effect is negligible except in extremely basic solutions). It's due to the ground glass joints on the bottle neck & stopper. These joints are designed to be so closely fitting that they are almost gas-tight, and as a consequence the two dry surfaces can get stuck together sometimes. This problem can be exacerbated if a solution of something gets in/around the joint, especially if solids start to precipitate out in the joint itself. If this happens try soaking the entire joint in hot water for a while, then tapping the stopper/joint to loosen it. Sometimes heating the joint with an air gun can achieve the same effect (although this only works if the joint is dry inside).

Murray Kelly · Apr 30, 2021

John-s, an old friend (a pharmasist) taught me a trick to get glass stoppers out.
Hold it by te stopper a cm off the table and tap the bottle gently with another one and the resonance will free up the stuck stopper.

Raghu Kuvempunagar · May 1, 2021

Alan Johnson said:
Maybe this is why a metol version of Rodinal is not sold, short shelf life.

Would a reasonably small amount of an auxiliary developing agent like catechol or hydroquinone extend the shelf life of concentrated Metol developer? IIRC @Pixophrenic was doing some experiments along these lines and I don't know what his conclusions were.

john_s · May 1, 2021

Murray Kelly said:
John-s, an old friend (a pharmasist) taught me a trick to get glass stoppers out.
Hold it by te stopper a cm off the table and tap the bottle gently with another one and the resonance will free up the stuck stopper.

Thanks Murray. I don't use them these days so I probably won't get around to trying that. Some were very stuck indeed. Hot water often helped. It seemed worse with developer (alkaline) and never fixer (acidic in the olden days) so I attributed the sticking to the dissolution. So perhaps it was just the tendency of the liquids to precipitate, although I always topped up with fresh water before putting in the stopper in order to minimise that.

Pixophrenic · May 1, 2021

Raghu Kuvempunagar said:
Would a reasonably small amount of an auxiliary developing agent like catechol or hydroquinone extend the shelf life of concentrated Metol developer? IIRC @Pixophrenic was doing some experiments along these lines and I don't know what his conclusions were.

Well, indeed on February 4, 2019 I made a preparation of Kalogen with reduced hydroquinone, metol/HQ=3:1. This change resulted in approximate doubling of development time. Initial dilution of 1:50 developed FP4 to adequate density in 12 minutes. It was stored in tightly closed tubes filled to the top. The last test of this variant was done on July 1, 2020. This time Kentmere Pan 100 was developed to adequate density in 1:25 dilution for 9 minutes. Then I sort of lost interest in this project, because other MQ storage projects were doing as good or better than this one. I may still have a portion or two around, also of original Kalogen and Gainer's "metolal" (with reduced alkali). it was obvious that such a preparation keeps quite well when stored as much as possible in the absence of air, but an open portion will discolor from the top. It was also obvious that after a long storage time gap one cannot trust that it did not lose some activity despite no change in appearance, so clip tests are necessary.

Pixophrenic · May 3, 2021

Raghu Kuvempunagar said:
Would a reasonably small amount of an auxiliary developing agent like catechol or hydroquinone extend the shelf life of concentrated Metol developer? IIRC @Pixophrenic was doing some experiments along these lines and I don't know what his conclusions were.

This is a different reply to the same question, because it occurred to me that Raghu made a hint on our private little conversation on Edwal 12 here. Also, previously I had no time to read the whole thread. Sorry to be patronizing, but there is a difference between storing a developer with sulfite as principal preservative in the (near) absence of air and storing a half-full bottle with a developer, which keeps on in spite of the continuous air intake during occasional use. A third case is a working developer that is used from time to time and returned to the same vessel (the most challenging). In my other storage experiments I noticed a group of various historical developers called "pyramid", because they contain 3 developing agents (sorry, Mr Schwalberg), wherein one actually contributes to the image, the second one regenerates it, and a third one regenerates the second.

Edwal 12 is one such example, but I also found that combinations of metol-HQ-glycin, p-aminophenol-HQ-p-phenylene diamine, phenidone-HQ-glycin and a number of others do keep rather well in half-full bottles and generally better than respective two-agent combinations. In each case it does not mean that activity stays at 100%, but it drifts down slowly enough, to add, for example, a minute per every month stored. The problem with these tests, fairly obvious, is that if you start some storage test, you keep silence online and come back after a year or two. It is an inefficient way to test "storage extenders". I think, however, but have not tried it systematically, that a good model system is a developer based on amidol or pyrogallol which decomposes rapidly, and extending the life of, say, an amidol developer from a couple of days to retaining 50% of activity in a month would be an achievement.

Otherwise, I second the opinion expressed above that a proper vessel with a proper closure is at least as important as the chemical composition.

Raghu Kuvempunagar · May 4, 2021

Pixophrenic said:
I also found that combinations of metol-HQ-glycin, p-aminophenol-HQ-p-phenylene diamine, phenidone-HQ-glycin and a number of others do keep rather well in half-full bottles and generally better than respective two-agent combinations.

This is very encouraging. Thanks for sharing your experience and insights. Much appreciated.

There's an interesting single part developer called Edwards 20X whose developing agents are Metol and Catechol. Despite having as high as 75g of Potassium Carbonate in it, the developer keeps well for at least a month, perhaps due to the high amount of Sulphite (100g), when stored full in tightly capped bottles. At least there's no quick death due to high alkalinity. I wonder if a small amount of PPD or Glycin can extend the shelf-life further. But here's the catch. Adding a third developing agent changes the character of the developer and might not offer the same image quality as the original developer. To alter the proportions of the ingredients so that the three-agent developer gives nearly the same image quality as its two-agent parent is a challenging task in itself. In the particular case of Edwards 20X, it's possible to make it a relatively long lasting 2 part developer by taking carbonate out though I would have loved to have a long lasting single part version.

relistan · May 6, 2021

Raghu Kuvempunagar said:
This is very encouraging. Thanks for sharing your experience and insights. Much appreciated.

There's an interesting single part developer called Edwards 20X whose developing agents are Metol and Catechol. Despite having as high as 75g of Potassium Carbonate in it, the developer keeps well for at least a month, perhaps due to the high amount of Sulphite (100g), when stored full in tightly capped bottles. At least there's no quick death due to high alkalinity. I wonder if a small amount of PPD or Glycin can extend the shelf-life further. But here's the catch. Adding a third developing agent changes the character of the developer and might not offer the same image quality as the original developer. To alter the proportions of the ingredients so that the three-agent developer gives nearly the same image quality as its two-agent parent is a challenging task in itself. In the particular case of Edwards 20X, it's possible to make it a relatively long lasting 2 part developer by taking carbonate out though I would have loved to have a long lasting single part version.

It seems like with the right pH and right agents you could hit a spot where you keep the pH below the threshold where the third agent became active as a reducer but was still able to act as a regenerator. For example, if you keep the pH below 9 you will prevent any real activity from glycin, p-aminophenol, catechol, or hydroquinone (Source: Haist. But he doesn't list ascorbic acid). They can still act superadditively below that pH where appropriate. In the developer you mention above, catechol being present means it likely already has a reasonably high pH, though. But, if it's below 10 you might still make use of hydroquinone as a 3rd agent without direct effect on the image. The additional superadditive effect with metol might still have a small but noticeable impact.

Pixophrenic · May 7, 2021

Raghu Kuvempunagar said:
This is very encouraging. Thanks for sharing your experience and insights. Much appreciated.

There's an interesting single part developer called Edwards 20X whose developing agents are Metol and Catechol. Despite having as high as 75g of Potassium Carbonate in it, the developer keeps well for at least a month, perhaps due to the high amount of Sulphite (100g), when stored full in tightly capped bottles. At least there's no quick death due to high alkalinity. I wonder if a small amount of PPD or Glycin can extend the shelf-life further. But here's the catch. Adding a third developing agent changes the character of the developer and might not offer the same image quality as the original developer. To alter the proportions of the ingredients so that the three-agent developer gives nearly the same image quality as its two-agent parent is a challenging task in itself. In the particular case of Edwards 20X, it's possible to make it a relatively long lasting 2 part developer by taking carbonate out though I would have loved to have a long lasting single part version.

There is indeed a number of ways how this developer can be made longer lasting, take away the potash, take away the catechol etc. On some films, you could even use it as 2-bath. I think, though, that in this particular developer catechol is the protectant of metol, not so much a developer. You would need a lot more of it to contribute to the image, as it is not super-additive with metol. This one IMO is a dilute metol developer working at high pH, just like the Jarai metol-phosphate developer I posted elsewhere in the resource.

Raghu Kuvempunagar · May 8, 2021

Pixophrenic said:
There is indeed a number of ways how this developer can be made longer lasting, take away the potash, take away the catechol etc. On some films, you could even use it as 2-bath. I think, though, that in this particular developer catechol is the protectant of metol, not so much a developer. You would need a lot more of it to contribute to the image, as it is not super-additive with metol. This one IMO is a dilute metol developer working at high pH, just like the Jarai metol-phosphate developer I posted elsewhere in the resource.

This is entirely plausible and it never struck me that Catechol could be working as a protectant in this developer. Will take a look at the Jarai developer.

esearing · May 8, 2021

Over the last couple of years I have been using Pyrocat M which is Cachetol + Metol and it performs much like Pyrocat HD which uses Phenidone as the secondary developer. Pyro-M part A lasts about 1 year in a less than full bottle. You can tell when it goes bad because when you mix it with Part B it turns Blue instead of the normal pale brown. Part A and B are mixed just before use and used one shot. Like HD, various dilutions can be used semi-stand , EMA, or normal 1:1:100 ( I have not tried rotary but should be similar at 2:2:100). I keep the raw Metol and Cachetol in their original plastic container, sealed with electrical tape, but will likely buy smaller quantities next time. Part B from the HD kit works fine with Pyro-M Part A.

Alan Johnson · May 10, 2021

Here's Ryuji on the subject of Plastic Bottles and which type is preferred:
http://web.archive.org/web/20050306213813/http://silvergrain.org/Photo-Tech/plastic.html

Pixophrenic · May 11, 2021

relistan said:
It seems like with the right pH and right agents you could hit a spot where you keep the pH below the threshold where the third agent became active as a reducer but was still able to act as a regenerator. For example, if you keep the pH below 9 you will prevent any real activity from glycin, p-aminophenol, catechol, or hydroquinone (Source: Haist. But he doesn't list ascorbic acid). They can still act superadditively below that pH where appropriate. In the developer you mention above, catechol being present means it likely already has a reasonably high pH, though. But, if it's below 10 you might still make use of hydroquinone as a 3rd agent without direct effect on the image. The additional superadditive effect with metol might still have a small but noticeable impact.

This is a good point about whether an auxilliary agent is superadditive or not. I am afraid, though, that history went a way where no other developing agent of those easily procured is superaddivive with catechol. Can you name one?

relistan · May 11, 2021

Pixophrenic said:
This is a good point about whether an auxilliary agent is superadditive or not. I am afraid, though, that history went a way where no other developing agent of those easily procured is superaddivive with catechol. Can you name one?

No I can't but I was referring to the superadditivity potential of adding hydroquinone. He was referring to a developer that had metol and catechol and I saying that it might be possible to add HQ and get some recharge effect but because it's superadditive with metol it might not be a good fit because it might change the character of the developer rather than just recharging the metol. It was just an idea.

Raghu Kuvempunagar · May 12, 2021

Pixophrenic said:
This is a good point about whether an auxilliary agent is superadditive or not. I am afraid, though, that history went a way where no other developing agent of those easily procured is superaddivive with catechol. Can you name one?

Is Ascorbic Acid not superadditive with Catechol? I see the pair being listed as superadditive in some threads in this forum. Not sure I saw anything on this pair in Haist.

Metol, hydrolysis

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