Help required understanding Developers

[Timothy]

I have been studying developer formulae for some time and am contemplating mixing my own. I am not a chemist and do not understand the chemical jargon, which of course makes it harder to understand everything else. I am working on the idea of a negative developer containing Dimezone-s and Sodium Ascorbate as superadditive developing agents; Sodium Sulphite as preservative (I understand that it might have other effects, like acceleration and silver dissolving, depending on several factors); and Kodalk as accelerator. I notice that several others who have done similar recipes use TEA and some form of glycol, and sometimes use Ascorbic acid instead of Sodium Ascorbate. If I understand correctly, the Glycol is used to dissolve the Dimezone-s since this is difficult in water, but I can not understand the use of TEA. What is it there for ? And how can an acid form of Ascorbate be used. While we are on that subject, why is Salycilic Acid and even Boric Acid used in other versions of this developer ?
If I can get these things resolved, I would like to then concoct a print developer with Glycin or something similar. But I need to understand the answers to the above first.

 

[Lowell Huff]

Why are you using Dimazone s as your accelerator? What is the desired result?

 

[gainer]

TEA in water has a basic pH. Sodium or potassium ascorbate are not appreciably soluble in TEA, but the ascorbic acid is. Dimezone, phenidone and paraminophenol are soluble. A solution of dimezone and ascorbic acid in TEA has no developing activity until water is added. One can make a P+C+TEA solution that is sufficiently concentrated that 1 part plus 50 parts of water will develop most films to normal contrast in 15 minutes or less.

 

[Mike Wilde]

Tim, for a modest deposit I can loan you a copy of a book published mid 50's that helps explain some of the chemistry of developing agents.

Find some time to drop by and see if it is something you want to read more in depth.

I think it is called 'The Chemistry of Photography' by Hornsby. I don't remember it making big mention of ascorbate developign agents, though.

I'm down in the southwest corner of town, the Sheridan Homelands neighbourhood s of Dundas between Erin Mills and Winston Churchill.

Mike.

 

[Timothy]

Thanks for the info, but I am still confused. The TEA is basic in water, I understand, but why it is used in the first place, I do not. My understanding has always been that in most developers an alkaline environment was crucial. If the Ascorbate and Dimezone-s (or Phenidone, Metol, Paraminophenol, etc.. ) are basic, and the sodium sulphite works as preservative, and the Kodalk works (as accelerator) without changing the pH, then what purpose is the TEA there for ? And if the pH must be kept at a high level, how can an acidic form of Ascorbate work ? Is the TEA acting as a kind of preservative, holding the developing agents in solution, in an inactive state, until the water is added ?

 

[Timothy]

Hey Mike,
Thanks, that is a great offer. Considering how close by, we really should do some collaborating. I am in the darkroom nearly every day these days.

 

[CBG]

You might find the "Film Developing Cookbook" and the "Darkroom Cookbook" each helpful to answer your questions. What you ask is all pretty much answered in those books and through poking around APUG using the search feature.

 

[gainer]

Thanks for the info, but I am still confused. The TEA is basic in water, I understand, but why it is used in the first place, I do not. My understanding has always been that in most developers an alkaline environment was crucial. If the Ascorbate and Dimezone-s (or Phenidone, Metol, Paraminophenol, etc.. ) are basic, and the sodium sulphite works as preservative, and the Kodalk works (as accelerator) without changing the pH, then what purpose is the TEA there for ? And if the pH must be kept at a high level, how can an acidic form of Ascorbate work ? Is the TEA acting as a kind of preservative, holding the developing agents in solution, in an inactive state, until the water is added ?

TEA is a good solvent. I could have, and indeed did, use propylene glycol to make a concentrated solution containing phenidone or dimezone and ascorbic acid. Diluting that solution with water would not provide the alkaline environment needed by the ascorbic acid-dimezone superadditive pair, so a separate alkaline solution was required.

Sodium sulfite is not required as a preservative when TEA or glycol are used as solvent. They are non-ionic liquids until water is added. Kodalk DOES change the pH.

There is another experiment you can try. Mix a very small amount of the dimezone with a larger amount of ascorbic acid in water. Add sodium or potassium carbonate until pH becomes about 9.5. You will see that this solution is a good developer. However, it must be used soon after mixing or it will oxidize, as it has no sulfite. If you add enough sulfite, you may see two results. The developer will last longer in storage, and the grain may be less noticable.

If you make a PC-TEA stock solution and measure its pH, you will find it to be near neutral. If you add 50 parts of water to 1 part of PC-tea, you will find it's pH to be well above neutral. The TEA is a convenient way to store a concentrated stock solution of phenidone, ascorbic acid and alkali for long periods of time. Do not try to add sodium sulfite to the PC-TEA stock. It won't dissolve and it is not needed as preservative. If you want to add sulfite to the working solution, be my guest, but don't expect any miraculous improvement.

If you search www.unblinkingeye.com for "Non-chromogenic Antiscorbutic Developers for Black and White Film" you will find a tale of my escapades that were triggered when I ran out of sulfite once.

 

[Timothy]

CBG: I have read both books you mention cover to cover several times. They do not answer my questions, unfortunately. I have been poking around the APUG articles and forums, with the search feature, and while some guidance has been found, I still have specific questions. But thanks.

Mr. Gainer, thank you. Your info is helpful, and I did read the article you linked. It appears that you have already formulated the exact developer that I was contemplating but have saved me the trouble of some "learning experiences". Where I am located, I think that Vit C is easier to get and cheaper than Sodium Ascorbate, so, since your experience shows that it works even better, I am grateful. Do you know of any advantage to using Dimezone-s or Metol, as opposed to Phenidone ? The "Cookbooks" seem to indicate that their efficacy as developers are about the same, but that the Dimezone-s should last longer. Do you have any comment ?

 

[Jordan]

Tim,

As you know, sodium ascorbate is just a salt of ascorbic acid. Some developers call for one or the other, but they function the same once the pH has been adjusted to the correct target level. The active developing agent is ascorbate ion -- how it gets into the solution is less important. Ascorbic acid tends to be more stable in the solid form and is generally easier to get, which is why many recipes call for it. These formulations call for more base to compensate.

(I would try to avoid thinking of "accelerators" in a developer. There are just too many misleading connotations. The principle is that developers need to be alkaline to function, and pH has a huge effect on activity, so we use various bases -- borax, metaborate, carbonates, sodium hydroxide, and as discussed below, triethanolamine -- to get the solution to the correct pH.)

Triethanolamine, as Pat mentions, is a base that can also serve as a viscous organic solvent. Ascorbic acid and phenidone (and its cousins) can be dissolved in it, and these organic solutions are protected from the oxidation that usually occurs in aqueous solutions. When diluted into water, the TEA loses its solvent role and simply brings the developer to an appropriate working pH.

Propylene glycol and ethylene glycol are also viscous organic solvents, but they are not bases. In one version of my "Instant MYTOL" formulation (posted here on APUG and on my website) I call for a solution of ascorbic acid and phenidone in a mixture of TEA and propylene glycol. This mixture contains just enough TEA to bring the final developer (once diluted) to the correct pH, but because that amount of TEA isn't enough to dissolve all of the ascorbic acid and phenidone, I added some propylene glycol to get everything into solution.

TEA is in some ways an ideal base for use in B&W developers. The negative-log acidity constant of its conjugate acid (pKa in chemical terms) is around 8, which is also the target pH for ascorbate developers like Xtol. Kodalk (sodium metaborate) is comparable and also a good choice.

Phenidone and dimezone-s are closely related. Dimezone-s has a somewhat different substitution pattern (a couple of methyl groups) that make it more stable to aerial oxidation but on a per-molecule basis, I think their activity is pretty close. From what I recall, dimezone-s was primarily invented to get around the patents covering phenidone. Neither are acidic or basic. Metol and hydroquinone are very different beasts and interact differently with other developing agents.

Sodium sulfite plays many roles in a developer, but from the point of view of formulation design, it's important to remember that it itself is somewhat alkaline and will raise the pH of solutions. In some developers (D23 and the Microdol / Perceptol types) sodium sulfite is the only base present.

Boric acid is sometimes used in combination with metaborate or borax to adjust pH. Salicylic acid is a chelating agent for metal salts that some ascorbate developers use to prevent "sudden death" by metal-catalyzed oxidation.

I hope this information sets you on the right path. I think getting a handle on acids / bases, pH, what happens when substances are dissolved in water, etc. would really help. Without this understanding, you may find developer formulation pretty frustrating.

 

[Timothy]

Wow ! That cleared a lot up. I had seen your recipe for Mytol and the variations, but did not understand what was going on. Now I see that I was misunderstanding the role of some of the ingredients. It has been mentioned that this topic has been covered so many times and there are so many sources yada yada .... , but this is the first time anyone has stated clearly why both glycol and TEA would be in the same recipe (first that I have seen, anyway). Your explanation of why an acidic form of developing agent can work is also helpful. It would appear that the PC-TEA formula is really the one that I was looking for all along.

Thanks,