Superadditivity in developers - and beyond

sanking · May 9, 2007

Alan Johnson said:
I mixed an ascorbate clone of FX-1 where sodium sulfite was replaced by sodium ascorbate: Metol 0.5g ,Sodium Ascorbate 5g ,Sodium Carbonate 2.5g ,water to 1L ,pH about 11. Delta 100 was developed in this 18m 68F. It gave somewhat overdeveloped negs with a high EI.
It is known from Crawley's experiments that if there is no sulfite the action with metol and carbonate alone is very slow.Therefore it follows that both the sulfite in FX-1 and the ascorbate in the clone must be participating in the development,but if by chemically similar reactions seems not to be known.
BTW this clone of FX-1 is similar to a developer listed by Patrick Gainer in his article "Vitamin C developers" at Unblinkingeye.com.

You write that the ascorbate clone of FX-1 gave a high EI. How did you measure this, by comparision to another developer? In my experience valid comparisons of EI require very tight controls in exposure and development.

Sandy King

gainer · May 9, 2007

I would not have developed Delta 100 that long in that formula. I would have guessed at most 10 minutes. However, the point that the development with Metol-ascorbate-carbonate is very vigorous is made. The trouble with trying to compare it with Metol alone is that aerial oxidation will happen very rapidly without some antioxidant.

Metol and sulfite in water are the only ingredients of D-23, which is quite active. If you were to develop Delta 100 in D-23 for 18 minutes you would also get overdeveloped high contrast negatives, I'll wager. Sodium ascorbate doesn't give as much pH as sodium sulfite, but if you were to add enough borax or metaborate to equalize the pH, I'll bet you will get the same activity with much less ascorbate, even though the molecular weight of ascorbate is considerably lower than that of sodium sulfite and should need more grams to get the same number of molecules.

I have to disagree that sulfite restores hydroquinone. The data in Mees & James show that it forms the hydroquinone monosulfonate but increases induction period and reduces rate of increase of contrast. If you want to try a hydroquinone-sulfite developer without added alkali, go ahead. I think you might have to wait all day for somethiong to happen. In fact, I think I will go and do that now.

Alan Johnson · May 9, 2007

Sandy,
Actually I was more interested in an approximate comparison of sulfite and ascorbate at this stage and as you say the EI measurement requires tight controls and only an approximate idea was obtained.I keep a roll of Delta 100 exposed to the same scene,average metering, sun/shade,EI 32 to 125 at 1/3 stop intervals,compare different developers using a loupe on the shadow detail against a light.I get about EI 80 for D76 1:1, the clone gave about EI 125 but was overdeveloped.
Mainly it's interesting the sulfite and ascorbate are both superadditive with metol but it's not known if in the same way.

Photo Engineer · May 9, 2007

Again, I refer you back to Mees and James Alan.

Chemical reactions are often slow. They can be sped up considerably by removing one of the products from the mixture. So, Metol is slow to oxidize, but add sulfite and it speeds up the oxidation. The same is true of HQ, it is slow to oxidize but it speeds up with sulfite. This is NOT superadditivity, but merely shifting the balance of a chemical equation. (if you substitute the word 'develop' in the above for the word 'oxidize' then you have the nature of the reaction in a developer).

In Mees and James they offer proof by using a different oxidant and demonstrating the same effect in the presence and absence of sulfite as we see in a developer. They show that this reaction is general, not just specific to a developer solution.

Mixing Metol and HQ together gives a synergistic reaction (superadditivity) that is different than the effect of sulfite. Sulfite speeds up this reaction as well, but by changing the reaction constant.

A + B * K = C where K is a constant. A and B are an oxidant and reductant respectively and C is the oxidized B (oxidized reductant).

A + B + D * K * KK = C + D = E where K is the original constant and KK is the constant supplied by removing C from the right of the equation by the action of D. Therefore, in the second reaction D = sulfite and C = Quinone and E = HQ monosulfonate.

This equation is a simple, non-balanced version of the redox reaction of HQ in the presence of silver halide and with and without sulfite. It is not even written in classic chemical terms. In those terms the "=" is changed to an arrow "->" or a double arrow (one in reverse "<-") with "K" above the arrow and "KK" or K1" below the reverse arrow plus other modifications. These cannot easily be shown without graphics.

PE

Alan Johnson · May 9, 2007

PE,
I wonder if you would care to comment on speeding up the reaction by ascorbate. Did Mees & James know about this? By the explanation you quote metol and ascorbate would not be considered superadditive. Is that the picture?

Photo Engineer · May 9, 2007

I didn't say that.

Mees and James don't comment on Metol + Ascorbate superadditivity AFAIK, nor has Haist, but my memory may be faulty. There was so much done with HQ + Metol that that is what I remember. I do know that we used an EAA (Elon (Metol) Ascorbic Acid) developer for research purposes, and I believe that the formula is in Mees and James, if not Haist.

PE

gainer · May 9, 2007

Let's refer back to the graph I took from Mees & James that shows the effect on development by Metol of hydroquinone OR sulfite OR ascorbic acid at pH=8.7. The effect of hydroquinone is nil. The line is flat at each development time. The effect of sulfite at each development time increases with amount of sulfite, levelling off at about 0.05 moles/liter. The effect of ascorbic acid is the same.

What was missing from this graph that cannot be deduced from it is the effect of both hydroquinone and sulfite on development by Metol at pH = 8.7. I do not see that treated anywhere in the volume.

Photo Engineer · May 9, 2007

Superadditivity is addressed in CH 13 of Mees and James (P299ff) and Chapter 16. The discussion is touched off by using Phenidone as an example.

PE

gainer · May 9, 2007

Photo Engineer said:
Superadditivity is addressed in CH 13 of Mees and James (P299ff) and Chapter 16. The discussion is touched off by using Phenidone as an example.

PE

That discussion does not mention the presence of sulfite. How much of the activity is due to phenidone and sulfite?

Photo Engineer · May 9, 2007

Sulfite is not superadditive, it merely changes the kinetic equillibrium as I have described previously.

It can only do so, according to Mees and James, if it reacts with a product of the development reaction produced by one of the developers.

PE

psvensson · Jun 1, 2007

I'm a little surprised to see that you guys are getting development from M-C mixtures without sulfite. I've used MC-TEA for quite a while - wonderfully sharp and fine-grained results on Delta 400 - but it doesn't do a thing without some sulfite added to the water - I use two teaspoons, or about 10 g/l. I guess it could be an issue of alkalinity.

dynachrome · Jun 2, 2007

Superadditivity

I have used PC-TEA and there is no problem getting adequate development without sulfite. I think I used a slightly incorrect amount of ascorbic acid so my times for FP4+ at 1:50 at 68 degrees F were 13 minutes or longer. Whether some combinations give actual superadditivity or just seem that way is an academic question. Once you have the time/temperature/EI figures worked out, you are in business. I have read that hydroquinone has either very little activity or no activity below a certain temperature. That temperature might be about 60 degrees F. When the hydroquinone does get active I don't know whether its activity increases in a liner or non-linear way as temperature increases.

Even if digital photography had not advanced as quickly as it did, there would still have been pressure to reduce the toxicity of the chemicals used. Color processing was mostly done on a larger scale and for many years the spent chemicals were picked up and treated in some way rather than just being dumped somewhere in an unsafe way. There isn't that much large scale traditional b&w processing being done now. This makes it even more important for small scale users to learn how to handle the chemistry safely. I think there were three factors in the interest in phenidone over metol in recent years. The first was that phenidone is less toxic than metol. Secondly, even though successful developers combined phenidone with hydroquinone, ascorbic acid is far less toxic than hydroquinone. If you use PC-TEA you even eliminate the sulfite and the amount of TEA used in a 1:50 dilution is quite low. Finally, the newer technology films and the improved old technology films (like Tri-X) respond better to phenidone than the older films did. The increase in grain is not very apparent and the improvement in sharpness is welcome.

You can do a lot with PC-TEA and do it more safely than with Rodinal or pyro type developers. I think that if developing times were too long or if we were using large rubber tanks with replenishment then superadditivity would be more relevant in practical terms. I any case this thread has been interesting to read.

gainer · Jun 2, 2007

I have gone a little farther since last time. The combination of Metol and ascorbic acid gives the same activity as Metol and sulfite if the pH is 8.7, according to Mees & James. You can get close to that by a simple combination of 8.5 grams Metol, 8.8 grams ascorbic acid, 4 grams of sodium hydroxide and 10 grams of borax in water to make a liter. You can replace both hydroxide and borax with 28 grams of sodium metaborate (Kodalk will do). This combination should be very active. You will probably want to dilute it 1:1.
The ascorbic acid could be replaced by sodium ascorbate, in which case cut the hydroxide in half. However much borax you put in will not give pH much higher than 9.2. As little as 4 grams will give pH about 9.2. Sodium ascorbate is close to neutral. Have fun.

gainer · Jun 2, 2007

I should have mentioned that the hydroxide is sufficient to neutralize the sulfuric acid attached to the Metol and to convert the ascorbic acid to sodium ascorbate which is only slightly basic. The solution wouldn't do much developing without the borax.

We often substitute 14.5 grams sodium hydroxide plus 69 grams of borax in a liter of solution as 10% sodium metaborate. 276 ml of such a solution contains 4 grams of the hydroxide and about 20 grams of borax, whether you mixed it that way or from 27.6 grams of sodium metaborate. I have tested both ways.

gainer · Jun 2, 2007

I should also have said that this solution is not awfully much different from D-23 in activity.

gainer · Jun 2, 2007

METOL-ASCORBATE

gainer said:
I should also have said that this solution is not awfully much different from D-23 in activity.

I DON'T KNOW WHAT I'M INTO HERE, BUT HERE GOES.

gainer · Jun 2, 2007

Metol-ascorbate

This is my third try to get the attachments attached.

gainer · Jun 3, 2007

These attachments really belong with the article and chem recipe about Metol and ascorbic acid.

Zathras · Jun 4, 2007

gainer said:
I should also have said that this solution is not awfully much different from D-23 in activity.

Pat,

Do you have any idea what shelf life of the stock solution might be?

Thanks

Mike Sullivan

gainer · Jun 4, 2007

I haven't had it long enough to know, but I expect it to be quite long. If it is true that the role of the ascorbate at this pH is to replenish the Metol and not superadditivity, the ratio of remaining ascorbate to Metol will not be important. The pH and bromide content of used or aerated developer is more important. There wont be any bromide build up due to aeration, and most will use it one-shot so bromide won't be a problem. The rather generous quantity of borax wont allow much change in pH during one shot use. I'm planning to leave a pint or so in an open container to see if it's still good after a month or so.

Maine-iac · Jun 11, 2007

gainer said:
I have found that a small amount of ascorbic acid in, say, a Metol-hydroquinone solution seems to be capable of at least as much superadditivity as the MQ solution with sulfite. It will be a staining developer if used without sulfite, as would the combination of Metol-pyrogallol-ascorbate or Metol-catechol-ascorbate, or p-aminophenol-catechol-ascorbate. I only know these things from experiment.

Pat,

I've never tried using Vitamin C with an MQ developer for film; I have used it in paper developer concoctions, where the staining doesn't appear to happen. I'd be interested in trying it with film. What proportions of M, Q, and C do you use? What activator--carbonate? metaborate? borax? How long?

Larry

gainer · Jun 11, 2007

If you are interested in the stain, use the Pyrocat MC formula with hydroquinone instead of catechol.

You could use 2 grams of Metol, 5 grams of hydroquinone, 5 grams of borax, and 10 grams of sodium ascorbate to make a liter of working solution. It's D-76 minus sulfite plus ascorbate. If you don't have ascorbate on hand, mix 2 teaspoons of ascorbic acid and 1 teaspoon of sodium bicarbonate (baking soda) in a couple of ounces of lukewarm water and add it to the mix when the effervescence subsides. Treat it like D-76 and see what happens.

alanrockwood · Jul 29, 2007

The last week or so I have been experimenting with ortho litho film developed using dilute rodinal solutions modified with the addition of borax and sodium ascorbate. I used 400ml H20, 1/8 teaspoon borax, and 1/2 teaspoon sodium ascorbate. (Sorry for the mix of metric and non-metric measurements.) To this I added either 1ml or 2ml Rodinal.

I shot some scenes in the back yard on 4x5 film and developed two sheets together in a batch.

Just based on the look of the negatives and preliminary testing it seems that the 1ml Rodinal solution will give a graded contrast range if I rate the film at an EI of somewhere in the neighborhood of 1/4 to 1/8 and develop the film in the range of 6 minutes at 75 F with continuous agitation in a rotary processor. The 2ml rodinal solution seems just a bit too active. (In fact, 6 minutes of the 1ml solution might even be a bit too much development.)

I haven't tried doing many controlled densitometry measurements yet, but I might eventually.

Anyway, what makes these observations relevant to the present discussion is that 1ml of rodinal is not much developer, being just a fraction of the amount recommended to avoid developer exhaustion. Therefore, it would seem that such a small amount of developer would risk exhaustion, particularly at a Rodinal dilution of 1+400. However, I don't think that exhaustion was taking place. In fact, fully over-exposed film gave a Dmax of something like 2.4 (as I recall) using a densitometer, so I don't think there is any developer starvation going on. I presume that the ascorbate is regenerating the para aminophenol, preventing exhaustion of the developer.

I also think that the ascorbate is probably not operating directly as a developer. From what I have been able to learn by my limited reading, if ascorbate is operating directly as a developer one would expect some fog, but in this case there is essentially no fog. In fact, base plus fog on an unexposed piece of film was something like 0.04 density units. (Yes, I have the decimal point in the right place.) This would argue against direct developer action by the ascorbate.

I eventually hope to follow up with more controlled experiments, but I thought I would mention the results of my preliminary experiments.

Any thoughts on this?

gainer · Jul 29, 2007

IIRC there is a hint or two at this phenomenon earlier in this thread. I'm too lazy to look it up. The pH of borax is lower than that at which ascorbic acid will act as a developer, but it is still quite an antioxidant. As such, it regenerates most of the developers we consider as primary such as Metol, Phenidone and p-aminophenol. In the process, it causes the pH to be reduced, but given enough borax, the pH may not change enough to be noticable. Perhaps this action is not true superadditivity, but the combination of a small amount of p-aminophenol with a relatively large amount of ascorbic acid and enough borax to buffer out the changes of pH will be surprisingly active. One could start with 10 g sodium ascorbate and 1 g p-aminophenol in a liter and add borax enough to saturate the solution. It should do several rolls per liter. Phenidone is better because of its lower sensitivity to bromide.

alanrockwood · Jul 30, 2007

Pat,

Thanks for the comments. Reading the accounts of your experiments has been very influential in my thinking.

Alan

Superadditivity in developers - and beyond

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