Phenidone Ascorbate 2-bath developer

dancqu · Oct 28, 2006

gainer said:
I am pretty sure that the oxidation of ascorbic acid
to the dehydroascorbic acid can take place in acidic
solution, so that acidic pH alone is not a guarantee
of long life.

I believe it accurate to say that A. acid acts as a
reducing agent with regards to oxygen at any ph we
might encounter including it's own. I've measured it
at 2.3. From a source detailing the preservation of
pharmaceuticals I've read that sulfite and A. acid
share the same reducing potential at ph 5. Less
than that and the sulfite will preferentially
absorb oxygen. Ryuji may have sources
which will confirm. Dan

gainer · Oct 28, 2006

A neutral solution of P and C in glycol can be made by neutralizing the C with TEA. I don't remember the exact amounts, but you can figure them form the molecular weights, 149 for TEA and 176 for ascorbic acid. Pre mix with a tiny amount of water to get a slurry, then add glycol and phenidone to bring to desired volume. This might be the best way to make a PC "A" bath for 2 bath development. You can also mix A and B to get a single bath for comparison.

Photo Engineer · Oct 28, 2006

There are several things to consider here.

1. Do the stock solutions keep? If they do, then all argumets over this are moot.

2. Does the developer you make of them give you the desired tone scale? If they do, then again all arguments are moot.

3. Do the negatives give you the sharpness, speed and contrast you desire at the appropriate enlargement. If they do, then this controversy and all over any developer is settled.

The remaining problems are:

1. Did you keep the stock solutions properly or run a proper keeping test with or without oxygen etc. etc. etc? This will confound any keeping test and give mixed answers from all the testers.

2. Did you run careful exposure and sentitometric tests with over and under exposures and different films? If not, this will confuse the issue among the different observers.

3. Did you make pictures at different magnifications or with different formats? The change in macro vs micro contrast will further obfuscate results if one person used 35mm and another used 4x5.

These are things to consider in any developer design situation and across the varied people here, I venture to guess that just about every person will get a somewhat different answer.

That is why designing developers requires such an intensive, years long effort using a broad range of keeping conditions, processing conditions, films, formats and print sizes and why questions like this keep arising. There is probably no one out there that has ever tested a developer as thoroughly as Ilford, Kodak, Agfa or Fuji has.

You do your best, but questions and problems and differences will continue to arise and until one person does all of the above, these types of thread will continue to be posted.

I forgot to add: USE WHAT WORKS FOR YOU.

PE

Alan Johnson · Oct 28, 2006

First,there is theoretical speculation if the stock solution part A will keep.
My take: The solution at pH 5 may decompose by this Fenton reaction (I think this means a supply of oxygen must be present).The Fenton reaction is not pH dependent and there are no good disclosed stabilizers at pH 5 to stop it being catalysed by dissolved iron from the other photochemicals.
Is that right?

Photo Engineer · Oct 28, 2006

Go here to see that the Fenton reaction is not very active at alkaline pH due to the formation of metal hydroxides.

http://www.lenntech.com/Fenton-reaction.htm

But there are other reactions that might be applicable.

PE

Ryuji · Oct 29, 2006

gainer said:
Not mine. I don't remember whose. If I had the wherewithal to test the premise, I would leave a solution of sodium ascorbate and sodium sulfite open to air and test periodically to see which oxidized first. Personal experience, which is at best what you might call anecdotal, is that adding sulfite to a P-C developer doesn't do much to extend its tray life.

That comparison and your experience don't tell much, since there is much faster mechanism in action, which that oxidizes those agents by air. The latter mechanism is much faster than the oxidation rates by the mechanism we are talking about. In other words, none of your argument is relevant if you experiment in absence of a catalyst poison to kill the fast mechanisms.

In my ascorbate developers I always incorporate such agents to kill the catalyst actions of iron and other transition metals, so I get more practically relevant results.

It all depends on which is the more active antioxidant, I suppose.

That's irrelevant again. The preservative does not have to work by superadditive mechanism like regeneration of developing agents. In reality, there are agents that have no reducing power at all but still act as a mild preservative.

I do know that one molecular weight of ascorbic acid will require one mole of oxygen for complete conversion to the dehydroascorbic acid, while one mole of oxygen will oxidize 2 moles of sulfite to the sulfate.

That's irrelevant again. In reality, the oxidation reaction is much more complicated, and it involves free radicals and multiple reaction pathways.

Ryuji · Oct 29, 2006

Alan Johnson said:
First,there is theoretical speculation if the stock solution part A will keep.

Why theoretical? Before I got insight into the catalytic oxidation of ascorbate, I experimented with all known tricks including split stock technique to prolong the shelf life of the developer solution. I know it doesn't work unless you add a stabilizing agent that poisons the redox catalysts. But then with a suitable stabilizing agent I have no problem getting practical shelf/tray life with more convenient single-stock ascorbate developers.

I have many compounds for stabilizer for many pH ranges. They are usually heterocyclic nitrogen compounds. They are difficult to buy unless you have a business account with scientific lab supplier or an industrial chemical supplier. I may try to convince Digitaltruth to carry some fo these agents but it entirely depends on their market analysis and their business priority.

Also, Fenton reaction is pH dependent. I don't know where you read otherwise. Also, I don't know who said Fenton reaction is the only mechanism. Fenton reaction is one typical reaction of the kind, but it doesn't matter what reaction as long as a redox catalyst is involved to greatly accelerate the oxidative degradation of the developer solution. The goal is not to kill just Fenton reaction but to kill ALL of the undesirable reactions.

dancqu · Oct 29, 2006

Ryuji said:
...greatly accelerate the oxidative degradation...

Oxidative degradation: Copper sulfate will at levels
as low as one trillionth normal have a "noticeable effect"
on the oxidation rate of sulfite. My question: are there any
complexing agents which will reduce below that level the in
solution copper sulfate.

Developers are a main focus but what of other sulfited
chemistry such as hca. I can imagine a few are doing
their hypo clearing in a tray of sulfate. Dan

Photo Engineer · Oct 29, 2006

dancqu said:
Oxidative degradation: Copper sulfate will at levels
as low as one trillionth normal have a "noticeable effect"
on the oxidation rate of sulfite. My question: are there any
complexing agents which will reduce below that level the in
solution copper sulfate.

Developers are a main focus but what of other sulfited
chemistry such as hca. I can imagine a few are doing
their hypo clearing in a tray of sulfate. Dan

Dan, on the alkaline side, the Fenton reaction or indeed any alkaline oxidative reaction initiated by a metal is mitigated by its ability to form metal hydroxide.

Therefore, the metal in question should be at a high oxidation state to start with and then should not form a very insoluable hydroxide in the developer.

PE

Jordan · Oct 29, 2006

I've been reading some older (1940s, 1950s-era) texts on qualitative inorganic analysis lately. Although a lot of the techniques have been superseded, they're a good way to learn "descriptive" chemistry. Something that keeps coming up in the chemistry of Fe(III) is its avidity for fluoride ion -- F- forms such a strong complex with Fe3+ (stronger than CN-, IIRC) that the iron no longer participates in its characteristic reactions (even with chelating ligands).

I wonder if anyone (Ryuji?) has investigated the use of F- as a preservative in ascorbate developers, or more significantly, whether fluoridated water supplies make a difference in the working life of ascorbate developers.

gainer · Oct 29, 2006

Sometimes I think the best way to get Suzuki to show his true brilliance is for me to post an ignorant remark.

Ryuji · Oct 29, 2006

dancqu said:
Oxidative degradation: Copper sulfate will at levels
as low as one trillionth normal have a "noticeable effect"
on the oxidation rate of sulfite. My question: are there any
complexing agents which will reduce below that level the in
solution copper sulfate.

Copper is much less PITA than iron. One can use DTPA, EDTA, NTA or most conventional amine polycarboxylic acids to inactivate its redox catalysis. Iron is a completely different story and it's the real PITA.

Developers are a main focus but what of other sulfited
chemistry such as hca. I can imagine a few are doing
their hypo clearing in a tray of sulfate.

I've been doing that for some time. My wash aid solution (Silvergrain Clearwash) incorporates my "stabilizing agents" that preserve sulfite in the solution at pH 7.

Ryuji · Oct 29, 2006

gainer said:
Sometimes I think the best way to get Suzuki to show his true brilliance is for me to post an ignorant remark.

Please don't. That just irritates me.

Ryuji · Oct 29, 2006

Jordan said:
I wonder if anyone (Ryuji?) has investigated the use of F- as a preservative in ascorbate developers, or more significantly, whether fluoridated water supplies make a difference in the working life of ascorbate developers.

I've read fluorides complex iron very strongly, but I've not actively looked into that route because the reaction of fluorides are not very specific to iron. Ideally I want some agent that inactivates iron catalysis without having any ill effect to silver halide developing process. Also, agents that react with alkaline earth cations are less desirable because the effective concentration of the active compound may fluctuate a lot depending on the quality of water supply.

Jordan · Oct 29, 2006

Ryuji -- Fair enough. But the second part of my comment still applies, I think -- that the F- content in water (which varies widely throughout the world) may have something to do with the working life of ascorbate developers (when they are mixed with tap water, obviously).

The fluoride concentration in municipal water (where it is fluoridated) seems to be on the order of 0.5-1 mg/L, which is around 0.03-0.05 mM. If the association constant for F- and Fe3+ is as high as they say it is (I'll try to get a number tomorrow), that has to be significant for any Fe3+-catalysed ascorbate oxidation.

I'll let you know if I read anything interesting.

Photo Engineer · Oct 30, 2006

Jordan, there are complexing agents that will dissolve even iron hydroxides from solution and entirely inactivate them. I have imbibed ferric and ferrous solutions into paper, and then into hydroxide to precipitate out the hydroxide. I have then had them analyzed for iron content.

After treatment with these special chelating agents, the iron orange colorization vanished. In some cases, the iron hydroxides were dissolved and in others it was there but highly chelated and colorless.

PE

Alan Johnson · Apr 23, 2007

I revived this thread to report that the formula given at the start does not work.The basic problem is that carry-over from bath A to bath B (about 20ml) provides a concentration of phenidone-ascorbate in bath B sufficient to make bath B a good developer on its own.Development due to conventional 2 bath development with the developer absorbed in the film is not detected.
I tried reducing ,separately, the phenidone and ascorbate concentrations,but at about half the original concentrations the negatives get thin and 2 bath development is not found.All tests 5min+5min 70F.
A seperate test of Thornton's 2 bath developer showed minimal amount of development in carry-over,highlights exhaust as 2 bath developer should.No problem with this.
This info may be of use to anyone trying to formulate a 2 bath phenidone ascorbate developer if that is possible.

Roger Hicks · Apr 23, 2007

Dear Alan,

Hydrolysis is a known concern with some developing agents, especially the original Phenidone. Don't know if that's the case here, but it's worth mentioning.

Cheers,

R.

Phenidone Ascorbate 2-bath developer

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