Why are developers so unstable?

RattyMouse · Nov 18, 2014

I'm curious to learn why photographic film developers are so unstable? Solutions of D-76, XTOL, and others start turning colors in relatively short periods of time. Further, many concentrates are also unstable once the bottles are opened and head space develops.

I always assumed that oxidation was the primary reason why developers go bad. If this is true, why are anti-oxidants not used to prevent this from happening? Anti-oxidants are very powerful and can prevent oxidation under many extreme conditions.

Is it possible that anti-oxidants actually interfere with the developing process? That's about the only reason I can think that would preclude adding some anti-oxidants into developer formulations.

Thanks for any info!

Steve Smith · Nov 18, 2014

I think oxidisation is the main problem but I also thought that anti oxidants were part of most developers.

Steve.

jochen · Nov 18, 2014

Hello,
developers are chemical reducing agents who reduce Ag+ Ions to metallic silver. During this reducing reaction (chemists speak of "redox reaction") the developing substance is oxidized to mostly intensive coloured oxidation products. The developing substance can be oxidized also by the oxygen of the air. To prevent this, an antioxidant or stabilizer is used in all developers. This is in most cases sodiumsulfite, potassiumsulfite, sodium- or potassiummetabisulfite or in more modern types a triethanolamine/sulfurdioxide complex. These substances react with oxygen before the developing substance is oxidized. The antioxidants are also reducing agents but their rdeducing power is less than of the developing substance. You can only use stabilizers with a lower reducing power as otherwise they would reduce silverhalgonides too.
In D-76 there is plenty of sodiumsulfite (100 g/ltr.) because here it works also as a sort of solvent for silver to reduce the grain. AGFA Rodinal with p-aminophenol as developing substance and potassiumsulfite as stabilizer can be nearly black-brown and works well nevertheless instaed of its intensive colour.

RattyMouse · Nov 18, 2014

Thanks Jochen....now I understand. Too powerful anti-oxidants means a non working developer.

ruilourosa · Nov 18, 2014

Developers are not that unstable otherwise they would not work that well... D-76 is a paradigm of sucess and also x-tol, but yes d-76 (the original formula) can have some ph flutuations (i never really notest as i use everything so fast) and there were problems (very few) with x-tol black out in some kind of waters (mainly high iron waters).

if you are unhappy with these two i recomend you change to rodinal or some TEA dev they last ages and they are always ready to go

Rudeofus · Nov 18, 2014

RattyMouse said:
Too powerful anti-oxidants means a non working developer.

Not only that, but anti oxidants also suffer from oxidation. Their main purpose is to scavenge Oxygen before it attacks the compound you want to protect, and obviously the anti oxidant will be oxidized in the process. If you look at a typical Metol-Hydroquinone paper developer: first the Sulfite will go (turns to Sulfate), once the Sulfite is gone the HQ will convert to Quinone, and once the HQ is gone the Metol will become oxidized. Sadly for the developer, but very luckily for us humans, there will always be about 20% Oxygen around to do this.

darkosaric · Nov 18, 2014

That is why I (between other characteristics) like Rodinal and HC-110.

Xmas · Nov 18, 2014

Rodinal takes 25 years to mature in 1/4 full bottle, or mine was ok after...

Lamar · Nov 18, 2014

I've just "discovered" Rodinal in the last year experimenting with stand development. I was a die-hard XTOL guy but I've found I really like the Rodinal look for normal development as well. Good stuff, and convenient.

hdeyong · Nov 18, 2014

I'm with Darko, HC-110 works very much like D-76, (according to Kodak), and no aging issues.

Lamar · Nov 18, 2014

LOL....... Aged in oak barrels on a hillside in Tennessee......

Xmas said:
Rodinal takes 25 years to mature in 1/4 full bottle, or mine was ok after...

Xmas · Nov 18, 2014

Lamar said:
LOL....... Aged in oak barrels on a hillside in Tennessee......

One side of my family used to make 'the wee still' and their idea of aging was two tumblers one under the end of the still the other upside down over the lips.

This was neatly a century ago, when my mum was four, the first thing she was taught, was not answering revenue & customs questions.

The wee still was the proper name.

Sirius Glass · Nov 18, 2014

I do not have this problem with XTOL and replenished XTOL, maybe you should not keep the chemicals in the stable.

Thomas Bertilsson · Nov 18, 2014

Conversely, I have been surprised with just how stable developers are. In particular when they are replenished.

Over the years I have used three replenished systems. Xtol, Edwal 12, and Harvey's 777. Harvey's I'm still working on so I don't have enough experience, but take Xtol as an example:

I mixed 5 liter stock solution and kept two liters as working solution. For each roll of film developed I replenished 80ml stock. If I didn't develop film for two weeks I'd replenish 80ml anyway. This method worked well for about five years with the same batch of Xtol. Just mix another 5 liter kit when I ran out of stock solution.
Beautiful system. It never skipped a beat. I even kept concentrated Xtol much longer than six months once, and it was fine. I also didn't use the working solution for almost nine months once, and it was perfect when I started processing again.
I never used any fancy bottles either, in fact I used the plastic bottles and accordion bottles that so many condemn. Go figure.

Edwal 12 was equally stable and consistent. Harvey's 777 I haven't used enough to tell, but I'm almost all the way done with my second gallon kit and I'm getting super consistent negatives.

I guess it depends on your expectations what you'd call unstable. To me that thought has never even entered my mind. I have always been amazed with how stable the developers have been.

John Bragg · Nov 18, 2014

+1 for HC-110 here. Almost bomb proof like Rodinal, until it is diluted to working strength solution.

RattyMouse · Nov 18, 2014

Thomas Bertilsson said:
Conversely, I have been surprised with just how stable developers are. In particular when they are replenished.

I guess it depends on your expectations what you'd call unstable. To me that thought has never even entered my mind. I have always been amazed with how stable the developers have been.

I work with chemicals all day long and have for 20 years, making products that have to survive in VERY extreme conditions and last years doing so. Chemical developers, some of them, go bad at room temperature in as few as a couple months. That doesn't even remotely fall under the term stable in my eyes. Even HC-110, the famed most stable developer is clearly not entirely stable. My bottle, which is perhaps 13-14 months old, is now a very very dark red color, not the pale yellow that it was when I bought it. It still works nicely of course, but something has clearly changed and is continuing to change. It is so dark red now it really can't get a whole lot darker.

pentaxuser · Nov 18, 2014

RattyMouse;1725821 Even HC-110 said:
Presumably and to all practical effect, stable in the context of film developer means the ability to work as it did when first mixed irrespective of whether it has changed colour. I base this on your statement of "still works nicely".

I accept that if it has gone as dark as it can it raises the question of what signs you look for to know that it is close to exhaustion. Presumably developing the film leader first would be one way but other than that I have no idea

pentaxuser

RattyMouse · Nov 18, 2014

pentaxuser said:
Presumably and to all practical effect, stable in the context of film developer means the ability to work as it did when first mixed irrespective of whether it has changed colour. I base this on your statement of "still works nicely".

I accept that if it has gone as dark as it can it raises the question of what signs you look for to know that it is close to exhaustion. Presumably developing the film leader first would be one way but other than that I have no idea

pentaxuser

I've been told that HC-110 changes color with no effect on its ability to develop film, so I am not concerned by the color change. I was merely commenting that from a chemical stability point HC-110 is clearly not entirely stable. My bottle is just barely over 1 year old and many here report using bottles several years old without issue. So I am going to finish up my remaining 50 ml's or so and be done with it. I don't think I need to test before using.

Thomas Bertilsson · Nov 18, 2014

RattyMouse said:
I work with chemicals all day long and have for 20 years, making products that have to survive in VERY extreme conditions and last years doing so. Chemical developers, some of them, go bad at room temperature in as few as a couple months. That doesn't even remotely fall under the term stable in my eyes. Even HC-110, the famed most stable developer is clearly not entirely stable. My bottle, which is perhaps 13-14 months old, is now a very very dark red color, not the pale yellow that it was when I bought it. It still works nicely of course, but something has clearly changed and is continuing to change. It is so dark red now it really can't get a whole lot darker.

Yeah, but your comparison is not apples to apples. Film developers are NOT designed to survive extreme conditions. They are designed to withstand a very standardized type of condition, which is roughly room temperature, with as little light and oxygen as possible reaching it.

If you think they're unstable, how stable do you need them to be? If a bottle of HC-110 goes bad on you, you should shoot and process more film!

RattyMouse · Nov 19, 2014

Thomas Bertilsson said:
Yeah, but your comparison is not apples to apples. Film developers are NOT designed to survive extreme conditions. They are designed to withstand a very standardized type of condition, which is roughly room temperature, with as little light and oxygen as possible reaching it.

If you think they're unstable, how stable do you need them to be? If a bottle of HC-110 goes bad on you, you should shoot and process more film!

Right, but the developers *could" be formulated to last longer. My bottle of DD-X has gone green, or slightly yellow and it's not even a few months old. XTOL, from what I read, is not a very stable developer. My D-76 jug showed significant discoloring after 6-8 weeks.

Granted, I dont go to extremes to keep oxygen out of my containers so improvement can be made in my process. My question was from my chemist point of view, why are developers so unstable? Why can't they be formulated to last at room temp at atmospheric pressures? This is not an extreme condition. In fact, film developers degrade in extremely mild conditions.

The reason I'm told here is that stronger anti-oxidants would interfere with the developing process. I can accept that answer.

Rudeofus · Nov 19, 2014

One thing you observe is the discoloration of Phenidone/Dimezone-S. These compounds in their oxidized form have very intense color in trace quantities, that's why some discoloration of HC-110 won't matter.

In the end you have to consider this: photographic development is a process, where a silver halide grain containing billions of silver ions will get reduced to metallic silver if it contains a cluster of three or more silver atoms, and it will not be reduced to silver if its biggest silver atom cluster has only two atoms. As a result you can detect months later whether a grain was hit by two photons in short succession - or not. I seriously doubt whether the robust chemical processes you work with offer the same level of sensitivity.

All this comes at a price: the number of compounds you can successfully use for this purpose is small, and the good ones may not be a stable as Ferrous Sulfate.

jochen · Nov 19, 2014

Hello,
developers with high pH-values are oxidized easier than such with lower pH. Some developing substances are more stable (4-aminophenol), others are very unstable (amidol, pyrogallol). Developers in high concentrations (Rodinal) are more stable than diluted solutions. The use of well boiled deaerated water and a inert gas above the solution is the best way to a more stable developer. Together with correct regeneration machine developers could last nearly for years. In very alkaline (NaOH or KOH) lith developers with extreme high pH paraformaldehyde is used as antioxidant which forms formaldehyde.

Thomas Bertilsson · Nov 19, 2014

RattyMouse said:
Right, but the developers *could" be formulated to last longer. My bottle of DD-X has gone green, or slightly yellow and it's not even a few months old. XTOL, from what I read, is not a very stable developer. My D-76 jug showed significant discoloring after 6-8 weeks.

Granted, I dont go to extremes to keep oxygen out of my containers so improvement can be made in my process. My question was from my chemist point of view, why are developers so unstable? Why can't they be formulated to last at room temp at atmospheric pressures? This is not an extreme condition. In fact, film developers degrade in extremely mild conditions.

The reason I'm told here is that stronger anti-oxidants would interfere with the developing process. I can accept that answer.

I am living proof that Xtol is a wonderfully stable developer. I have used it on and off for seven years, probably about 30 five liter kits. It has never skipped a beat. We used to use it at the professional photo lab I used to work for, with huge deep tanks. It was used because it was so consistent and easy to replenish and keep stable.

Otherwise, perhaps it would also make sense to consider the financial interests of the company making them. D76 and Xtol are both good for at least six months when stored properly. So is DD-X, but in all cases it is a good idea to evacuate air, to keep light away, and to keep them cool. If you fail to do so, then the developers will fail faster. That's also described in the data sheets of the manufacturers.
If they made developers that lasted forever, they would make less money. Compare a bag of D76 that can be purchased here in the US for about 6-7 US dollars to a bottle of Rodinal that can be had for about 15 US dollars. D76 makes a gallon of stock solution. If you dilute it 1:1 you can process about 12-16 rolls of film with it, depending on format. Rodinal most people use diluted 1:50, so out of 500ml you get 25 liters, or enough for 50-60 rolls of film depending on format. As a sales person, which developer would you rather sell if your income was based on commission?
Just another angle.

Alan Johnson · Nov 19, 2014

Rodinal type in absence of air lasted at least 62 years, see Azol:
(there was a url link here which no longer exists)

Metol in Neofin Blue in absence of air over 30 years:
(there was a url link here which no longer exists)

Phenidone in absence of air will slowly hydrolyze, see LFA Mason,Photographic Processing Chemistry. that is why it is often replaced by the longer lasting derivative Dimezone-S,which lasts a long time in Xtol as pointed out above.

Sodium Ascorbate, I have had a 50g/L solution in a full sealed bottle still active after 5 years.

Hydroquinone, IDK, but a mix of HQ and Metol in a sealed bottle went black rapidly at high pH when I tried to make a Rodinal substitute.

In presence of air they all oxidize once any sodium sulfite preservative is used up, if not in organic sovent like HC110 and the somewhat similar Ilford developers.

RattyMouse · Nov 19, 2014

Thomas Bertilsson said:
I am living proof that Xtol is a wonderfully stable developer. I have used it on and off for seven years, probably about 30 five liter kits. It has never skipped a beat. We used to use it at the professional photo lab I used to work for, with huge deep tanks. It was used because it was so consistent and easy to replenish and keep stable.

Otherwise, perhaps it would also make sense to consider the financial interests of the company making them. D76 and Xtol are both good for at least six months when stored properly. So is DD-X, but in all cases it is a good idea to evacuate air, to keep light away, and to keep them cool. If you fail to do so, then the developers will fail faster. That's also described in the data sheets of the manufacturers.
If they made developers that lasted forever, they would make less money. Compare a bag of D76 that can be purchased here in the US for about 6-7 US dollars to a bottle of Rodinal that can be had for about 15 US dollars. D76 makes a gallon of stock solution. If you dilute it 1:1 you can process about 12-16 rolls of film with it, depending on format. Rodinal most people use diluted 1:50, so out of 500ml you get 25 liters, or enough for 50-60 rolls of film depending on format. As a sales person, which developer would you rather sell if your income was based on commission?
Just another angle.

You're still missing the point of my question. I was concerned with the scientific reasons behind the instability of developers. By *any* measure, most are very unstable materials. I formulate highly oxidizable products that can sit in an oxygen environment for years sometimes without degradation. Because of my background I wanted to learn why a photographic developer cannot do the same. I learned that from this thread, regarding why only weak anti-oxidants can be used otherwise you get no development activity. The developers get diverted towards reacting with the anti-oxidants, not the silver halide.

Cost to the end user had nothing to do with my question. I was thinking and asking from the point of view of a formulation scientist. I make products for customers and they *demand* a long shelf life. Any product that I formulated that went bad in 6 months would be a complete failure. Replenishment is simply replacement of key additives. That is not stability, that is replacement. Would you consider your transmission fluid in your car highly stable if every 3 months you had to go to the shop, pull out 25% of the volume and "replenish" it? No, I don't think you would.

As I already said, I know all about methods to improve stability from a hobbyist point of view. That has nothing to do with my scientific query.

Why are developers so unstable?

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