A very low contrast, low pH, full speed POTA variant

Alan Johnson said:

The catechol-borax compounds have known formulae given in equations 4 and 5 below.
They seem to be present in very low concentrations in the developer formula given.
Borax is stated to form complexes with orthodiphenols only, ie not with pyro.
http://www.jbc.org/content/227/1/473.full.pdf

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Alan, is it possible what is meant is it must be at least di-phenol?

Here is the quote from Haist under Borate alkalis:

"These compounds (ie borates) should not be used with developing agents having two hydroxy groups ortho to eachother, as in catechol or pyrogallol. Borates react with o-dihydroxybenzene compounds to produce a reaction product that has very low developing action."

Since pyrogallol is a trihydroxybenzene compound and Haist includes it, I read this to mean as long as there are two hydroxy groups ortho to eachother, but not limited to two hydroxy groups).

Then again I might be in a little over my head here...

I am not the only one considers Haist got this wrong.
In the formula diagram in the link I gave,borax plugs neatly into the two OH groups on Catechol forming a complex.Pyro has an extra OH group that does not neatly fit,no complex is formed.
The practical consequence is that catechol borax gives a blank film,at least with metaborate,I tried it IIRC.Pyro metaborate works fine, it is of course found in PMK Pyro.

Interesting. Thanks for clarifying. Indeed it would be difficult to explain why PMK works ok if Pyro and Metaborate didn't jive.

It's misleading to look at a molecule such as pyrogallol and think of it as a 2-dimensional object. It is possible that the third hydroxyl group mechanically interferes with the formation of the adjacent borate moeity. Although this is usually seen with bulkier groups such as a isopropyl or t-butyl group. It is also possible that the electron density of the hydroxyl group also inhibits formation of the ester. One would have to run a few tests varying the borate concentration to see if this is true. I was not able to find mention of a pyrogallol borate ester online, which of course does not mean that one does not exist.

In accordance with my non-misleading theory you can find the formula for pyro metol borax posted on here.pH ~7.6.

Since I don't have a pH meter yet (but I'm working on it ), what do you suppose the approximate pH of this formula is:

20g sodium sulfite (anhydrous)
1g ascorbic acid
1g Dimezone-S
-----
1L

I just tried this one. I will post the curves tomorrow. I'm surprised by how apparently superadditive even this combo is. At the same 10:00 developing time I've been using for these formulas, it produced nearly the same contrast as the version with HQ, although with a flatter shoulder, slightly less toe contrast, and slightly lower base fog.

Once again Kendall-Pelts groups for ascorbic acid and dimezone predict that the combination will be super-additive.

Saturday Night Fever

So after a long time of promises I finally got around to do a few pH measurements for Michael, and I think they provide us with quite interesting food for thought:

1. Sodium Sulfite pH

In order to establish, what Sodium Sulfite would do alone in aqueous solution, I measured pH of Sodium Sulfite in various concentrations:

Conc. of Na2SO3 sicc.	1 g/l	2.5 g/l	5 g/l	10 g/l	20 g/l	40 g/l	100 g/l
pH at room temp.	9.08	9.24	9.36	9.48	9.50	9.51	9.49

As soon as we hit about 10 g/l, pH of Sodium Sulfite solution is independent of actual concentration.

It is, however, not independent of time: Within minutes it dropped from pH 9.60 to pH 9.50, there it stayed for a while but after about two hours it was down at 9.15 ! As I mentioned in previous postings, and as you will see in the next tables, Sodium Sulfite is an extremely poor buffer, and with just a bit of aerial Carbon Dioxide dissolved or Sulfite ion oxidized to Sulfate, pH will drop like a rock. Note, that this affects pure Sodium Sulfite solution, but not necessarily Sodium Sulfite solution with an additional acidic ingredient, like e.g. D-23.

2. Sodium Sulfite and Phenidone pH

Now let's add some Phenidone: dissolving Phenidone in quantity is a pain, and 1 g/l can mean you stir for half an hour or more. I therefore have two stock solutions of Phenidone ready: one with Propylene Glycol, another one in Diethylene Glycol. Before I moved on to the tests Michael actually wanted, I had to make sure that the solvent (PG or DEG) would not mess up solution pH.

Phenidone source	pH of 20 g/l Na2SO3 and 1 g/l Phenidone
powder	8.84
Phen in PG	8.81
Phen in DEG	8.83

The differences are small enough to be ignored IMHO. Remember we can't use PG if we have Borates in the mix. Not sure about DEG.


3. Sodium Sulfite and Ascorbic Acid pH

I claimed in some previous posting, that Ascorbic Acid will have given up one proton at the pH range we look at, so it will behave like a strong acid with one proton. In order to prove this, I compared Ascorbic Acid to same mole of other compounds which are known to be strong acids at pH 7-10: Sodium Bisulfate, and Sodium Metabisulfite. Note, that Sodium Metabisulfite will, once dissolved in water, release two protons, so we need half the moles of Metabisulfite than Bisulfate. Here are the pH values measured:

Compound	concentration	resulting pH
Ascorbic Acid	1 g/l	8.18
NaHSO4	0.682 g/l	8.21
Na2S2O5	0.539 g/l	8.18

Given, that it was quite tough to measure the small amounts needed for 50 ml test batches, and the extremely good match of the measured pH values, we can safely state that Ascorbic Acid behaves like an acid in the pH range we look at, and that it will cause no additional buffering.


4. Michael's developers


Next, let's add the compounds that Michael wanted to base his low contrast developer on. Here are solutions and measured pH:

Composition	solution pH
20 g/l Na2SO3 + 1 g/l Ascorbic Acid	8.18
20 g/l Na2SO3 + 1 g/l Ascorbic Acid + 1 g/l Phenidone	8.19
20 g/l Na2SO3 + 1 g/l Hydroquinone	8.98
20 g/l Na2SO3 + 1 g/l Hydroquinone + 1 g/l Phenidone	8.73
20 g/l Na2SO3 + 1 g/l Catechol	8.72
20 g/l Na2SO3 + 1 g/l Catechol + 1 g/l Phenidone	8.63

The result shouldn't be overly surprising: we know from above that Phenidone is a mild acid at the pH we use it at, so the soup with Phenidone is lower in pH than the version without. Since Ascorbic Acid is a strong acid for our purposes, Phenidone doesn't affect it, whereas it does affect the weak acids Hydroquinone (pKa1 = 9.9) and the slightly stronger acid Catechol (pKa1 = 9.25).

Rudeofus - I can't thank you enough for this information. Very interesting indeed, and it definitiely highlights my need for a pH meter as all sorts of follow up questions came to mind regarding Metol etc., and the difference if any between Phenidone and the derivative I've been using (Dimezone-S, which by the way I'm not finding any easier to dissolve than Phenidone, unless you grind it up first). Apparently more Dimezone by weight is required when substituting it in place of Phenidone.

I'm also wondering if the pH of the Pyrogallol version is similar to the HQ and Catechol versions.

It is interesting that when I tried the Ascorbic version I got nearly the same contrast as the HQ version at the same developing time, even though the pH is apparently significantly lower. The Ascorbic acid version at pH ~8.19 is in the initial target range I was hoping for (8-8.5). I'm hoping with some tweaks to the ratios I can get the same type of curve I got with the Pyro version, since so far that one seems to be closest to what I has looking for in sensitometric terms.

Thanks again for doing all this. Hopefully Gerald and Alan and others will have comments. I'm learning quite a bit here, and as I expected it is highly complex.

More experiments to come.

Michael R 1974 said:

I'm also wondering if the pH of the Pyrogallol version is similar to the HQ and Catechol versions.

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This source claims that Pyrogallol has a pKa of 8.9. This makes Pyrogallol more acidic than Catechol and Hydroquinone, although not by much. So I would expect a resulting developer pH slightly below the Catechol and a bit more below the Hydroquinone formula, but still higher than your mix with Ascorbic Acid.

Michael R 1974 said:

It is interesting that when I tried the Ascorbic version I got nearly the same contrast as the HQ version at the same developing time, even though the pH is apparently significantly lower.

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As you probably know, activity depends not only on pH, but also the inherent activity of the dev agent you use. Also note, that development itself changes pH of your soup, and likely by quite a bit because it is so poorly buffered.

If you really want a pH of 8.1, add a good buffer that actually maintains this pH.

I made some catechol version:

Sodium sulfite anh..........20g
Pyrocatechin....................1g
Dimezone-S.....................1g
Water to..........................1L
It is advisible to use rubber gloves for handling this solution IMO.

I took some pics of the shaded side of a tree against sunlit clouds.
APX at EI=50 metered for mid-tone was developed for a long time, 22min, to get the density up towards Xtol (Is that the idea?).
Reference was APX @ EI=50 developed in Perceptol.
Through a loupe I can see a little more shadow detail in the catechol version, it does not show well in the straight scans attached.

Alan, if you do such a test with extreme contrast, you have to account for lens flare, which means your shadows will lack contrast and detail even if you'd have an ideal developer giving you infinite ISO speed.

I encourage everyone to put a Stouffer wedge into your enlarger and make a print. Then contact print the wedge and see the difference.

Thus far I have been doing all the tests with wedges so that I can generate objective data. It makes it easier to compare things - at least the sensitometry part. But I am curious to try some field tests.

Alan: although I have not tested development times longer than 10:00, my guess is if you try to get normal contrast with these formulas you'll end up with fairly high fog. What I'm after here is very low contrast (~N-3 to N-4 in ZS terms) with full film speed, good toe contrast, and a relatively straight line that doesn't obliterate contrast in extreme highlights. In addition, the desired working pH is in the 8-8.5 range typical of most fine grain formulas. In short, a special purpose developer for extreme contrast reduction without the massive speed losses typically associated with severe minus or compensating procedures.

Rudeofus, re pH and development times etc., I completely agree pH is only one variable. The reason I was initially surprised though, is the conventional wisdom seems to be that all things being equal, the PQ superadditive combination is more efficient or "powerful" than PC. For example in the FDC the authors refer to what they call "weakly superadditive" combinations as desirable. They include Phenidone-ascorbic acid (referencing the work of Zawadzki/Dickerson) and Pyro-Metol and Metol-Glycin as examples of these versus more powerful combinations such as PQ. Then again, these characterizations might assume the more typical superadditive ratios encountered in general purpose developers (usually tiny amounts of Phenidone). So I might be on a different footing with the much higher concentration of Dimezone in these tests formulas. Of course superadditivity also varies with pH, so lots of variables here.

I'm also glad to know increasing the sulfite a little won't increase the pH. Perhaps more sulfite would result in slightly finer grain. But I haven't begun to look at image structure yet. And the sulfite level could impact contrast as well.

This continues to be a valuable learning experience.

Just to re

Even with 22min development the highlight density with the catechol version is less than that with Perceptol at 9 min.
With 13 min development the catechol negs look decidedly thin although shadow detail is better than Perceptol (not shown).
If you like there seems to be plenty of scope for increasing the development time upwards from 10 min.

Alan, it could be your catechol version performs differently than the Pyro, HQ and AA versions I've used so far. What is the ISO speed of the film you used? Also note Perceptol is known to be a speed-losing developer.

Did you see or measure more base fog density in the 13 and 22 minute development times with the experimental developer vs 9 minutes in Perceptol?

Thus far what the curves for my experiments are showing me at a 10:00 developing time with TMX 100, are:

1) Essentially the same effective film speed as when developed in XTOL 1+1 to a normal CI (ie full film speed). There are variations though, with the Pyro version giving the highest "threshold" densities but the ascorbic acid version giving slightly higher toe contrast.

2) Very pronounced contrast reduction vs normal development in XTOL. Here again the curve shapes vary somewhat across the experimental formulas. The Pyro version gave the straightest curve. The ascorbic acid gave higher toe contrast but more flattening of extreme highlight exposure values. So it is tricky to say which gave lower overall contrast since it depends on how it is measured (Gamma, CI, "Zone System"), etc.

Apologies for not having posted the ascorbic acid curve yet. Will get it posted as soon as I can.

More experiments and data to follow. And I'm hoping to get a pH meter shortly. Just have to decide which one will be easiest for me to use and maintain throughout this project.

Michael,

I found one of your developers seems to work and will continue to try it. IMO it is too early to go into details of practical use or comparisons.

There is one theoretical question-does your "full film speed" have a defined meaning?
A conventional method of defining film speed shown in the diagram in the link below does not appear to apply to low contrast developers.
http://en.wikipedia.org/wiki/Film_speed

Alan, that's an entire discussion on its own - and a complicated one, particularly concerning the theory and how it might be applied to developers like this which are "special cases". The case we have here is extreme, in which the curve is severely flattened without it shifting significantly to the right on the D/log-H plot. The ISO method is problematic here because the criterion ("triangle") of a target density increase over a specific log-H range is not satisfied. With general purpose developers, as contrast is increased or decreased, the Delta-X criterion results is smaller than expected speed changes. If one were to apply the fractional gradient method to the experimental formulas we've been testing here, we'd likely actually find an increase in speed vs the film's ISO.

Given this "special case", and the fact we need some kind of reference point, what I've been doing thus far with these developers is simply targeting a fixed density for the speed point (0.1 above FB+Fog). This is essentially the way Zone System testers find their speed point. Then, I'm comparing the exposure at that point to the exposure required to produce that density when the film is developed to a normal contrast index in XTOL (ie ISO speed within margin of error). If the test formula produces the same target density as the XTOL reference at the same exposure, then I'm saying based on the fixed density point criterion no film speed has been lost relative to the reference, even though total contrast has been greatly reduced.

Ultimately it gets more complicated than this depending on how contrast is measured etc., and we then get into tone reproduction, desired curve shape/local contrast etc. etc. But I had to start somewhere given the extreme case.

So having said all that, here is a more complete explanation of what I mean when I say full film speed in this case (for example referring to the fairly straight curve resulting from the Pyro version): Given appropriate circumstances, if this is the desired curve shape and contrast with TMax 100 (the test film), there is virtually nothing to be gained by giving more exposure than one would when developing the film to normal contrast in XTOL.

Attached is the graph including the test formula with ascorbic acid. Just to recap, development time was 10:00 for all test formulas (ie excluding XTOL) at 68F with agitation as described in the first post.

Michael,
Thank you for posting this. The Dimezone-S + Ascorbic Acid curve looks very similar to the curve from your original Dimezone-S + Pyro formula.
Could you elaborate on any perceived differences between the two? Anything you might expect from one vs the other? Image structure characteristics? As I've mentioned I'm very curious about and interested in this approach to "N-3/N-4" type scenes.

Shawn, over the next few weeks I hope to experiment more with these, and make some prints so that I can also try to evaluate relative graininess (although ultimately it will not be possible to objectively quantify things like granularity and acutance without microdensitometry - and that ain't gonna happen). I will post the results for discussion. Based on the pH values Rudeofus provided us, theoretically/superficially one might expect the ascorbic acid version to be slightly finer grained. But there are so many variables it would be unwise to speculate at this point.

The curve with the Pyro formula is "straighter", with almost zero toe. The ascorbic acid formula is slightly more typical/s-shaped: relative to the Pyro version it has slightly more toe in the very lowest exposure values (below ~Zone II) but more contrast in the shadow values above that and into the midtones. Above ~middle grey it has about the same gradient/contrast as the Pyro version, and then flattens out more in the extreme highlights. In fact, if you compare the shapes of the curve from the Dimezone-ascorbic test formula, and the two XTOL curves, they are very similar, which is interesting in and of itself given XTOL is a Dimezone-S/ascorbate formula (although the proportions and the rest of the formula are completely different.

Also, in terms of both tonality and image structure (graininess etc.), note so far these have been simply formulated experimental developers with simple 1:1 (by weight) substitutions along the way. None of these formulas are "optimized", just potentially promising starting points. The relative concentrations of the developing agents, sulfite etc. no doubt require some refinement before proper comparisons and evaluations can be undertaken. Also, the test formulas have so far only been used with TMax 100 - a fairly easy film to work with. A lot more work is required here.

Stay tuned.

I appreciate you taking the time to step me through this, Michael.

Michael R 1974 said:

Stay tuned.

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For sure!

If you have any questions at any time feel free. I'm learning too. I thought I knew enough about acids/bases and pH, but clearly I need to do more work on that. Luckily Gerald, Rudi, and Alan have been helping me out here.

Michael, can you tell me/us, why the regular Xtol curve looks so downwards bent? Can you check with a Stouffer wedge whether your densitometer gives you accurate numbers at high densities?

This is the type of curve I've always experienced with TMax 100 (specifically) and XTOL. In my experience it is as much a property of TMax 100 as the developer/agitation. The highlights have a gradual shouldering (the plot covers 16 stops) and develop to significantly lower densities at the highest exposure values in comparison to say TMax 400. The TMax 100/XTOL combination in particular seems to produce particularly strong shadow and midtone contrast and a long, gradual shoulder. I will dig up some comparitive curves I did a while back with Delta 100, TMax 100 and Acros in different developers, which may help. I think now that you mention this I will also run a few rolls of TMax 100 in D-76, which is more often the "reference" developer of choice. With respect to the densitometer readings, I always check it with the calibration samples, and with step wedges everything checks out.

Rudi - another thing I forgot in my previous post: recall there is also a slight "orange/red" tint in the highest densities with this film which, when read through blue filtration on the densitometer, results in a little more highlight contrast than the "white light" curves. You can see this effect if you go back to the first graph I posted in the thread in which I plotted readings with white, blue and green light. Initially I thought this might have been a small amount of Pyro stain, but I get the same results with all the test formulas, XTOL, etc., so I assume it to be a property of the film, which is why I didn't include these blue/green curves in subsequent plots.