Progress on XTOL-concentrate

[albada]

I don't know of any developer produced on a non-profit basis that contains a chelating agent to prevent hard water cloudiness.This includes all Crawley's published formulae, PMK Pyro,the Pyrocats. Gainer's PC-TEA etc.I have not come across any grumbles on the internet about cloudiness produced by these developers.

I hadn't thought of that, and thanks for pointing it out. Maybe such folks typically use distilled or DI water. Anyway, it's an easy test, so I might as well check if all that citric acid prevents cloudiness.

Is 99% TEA hard to obtain in the UK? This subject was brought up a few months ago, and I don't recall a clear conclusion. Does Mistralni sell 98% TEA? I think you can get it at Fototechnik Suvatlar in Germany. In the US, 99% TEA can be purchased from The Chemistry Store. For consistency, I suggest avoiding the 85% TEA sold by the Formulary.

A few months ago, PE wrote "...buffer capacity can be looked at as the total number of moles of alkali present in a solution." TEA is an alkali, and when used as the main solvent, it contributes a large number of moles and therefore should boost buffer capacity greatly. That's a strong advantage.

Today's Experiment -- reducing viscosity of TEA by mixing in PG:

I wanted to see how much propylene glycol (PG) needed to be mixed into TEA to get acceptable viscosity at cool temperatures. A water-bath kept temperature at 17C, simulating a cool darkroom in winter. A 28%-72% mixture of PG-TEA had reasonable viscosity at 17C. Dissolving powdered chemicals will boost viscosity a little, so I'd say 33%-67% (one third / two thirds) of PG-TEA would work well.

Mark Overton

 

[Rudeofus]

The wikipedia article on citric acid here says it's an "excellent" chelating agent.

Heavy Fuel Oil is a "great" fuel but I still wouldn't recommend it for your car. When I cleaned limestone residues from my sanitary installations with citric acid, it worked great, but at a temperature, pH level and concentration you would not want in your developer. My recommendation is you take the hardest tap water you can find (let some limestones sit in it for a week), add the amount of citric acid you use in you dev to this water, then add 100 g/l sodium carbonate. If you get precipitation, you likely need a stronger chelating agent.

I guess we don't know if citric acid will chelate well in a developer, so as PE says, tests must be run. Also, I understand that the Fenton reaction with iron will eventually destroy the ascorbate, but that takes days or weeks, and this is a one-shot dev, so I don't care about Mr. Fenton. Although if I can chelate the iron for free, I will.

I have read reports that Mr. Fenton sometimes takes days or weeks to do his job, but sometimes he is in a superhurry and finishes off all the ascorbate in an hour or so. Therefore I think you should pursue one of two options:

1. Distilled water is easier to get than most chelating agents, and quite cheap, too. Note, that your concentrate targets people who are very low volume developers, so the cost of distilled water should be irrelevant. If one roll of film fails due to evil Mr. Fenton, it's a pitty but most likely the damage done to humanity is of limited extent. Few pieces of great art come from a tiny portfolio.
2. Or use a chelating agent which takes care of all these issues (tap water impurities, iron) at once. If DTPA does not dissolve in the concentrate, you might mix it with the sulfite. Maybe Dequest 2010 does dissolve in PG and works well

 

[Alan Johnson]

Is 99% TEA hard to obtain in the UK? This subject was brought up a few months ago, and I don't recall a clear conclusion. Does Mistralni sell 98% TEA? I think you can get it at Fototechnik Suvatlar in Germany. In the US, 99% TEA can be purchased from The Chemistry Store. For consistency, I suggest avoiding the 85% TEA sold by the Formulary.



Mark Overton

I have not found a source of relatively pure and inexpensive TEA in the UK.
Mistralni.co.uk is not expensive but is the 85% grade.
Scichem.com sell 500ml 97% grade at GBP 16.07+VAT + ~GBP 12 shipping but need an email request stating what it is required for and details of the buyer whereupon they will decide to supply it or not.

BTW, I don't think a little cloudiness does any harm,I always get it from the carbonate in Pyrocat-HD with no apparent harmful effect.

 

[Photo Engineer]

Cloudiness, from a precipitate by hard water, can cause defects in the image of films. The small particles become lodged in the gelatin causing you to have specks of white in the final print.

PE

 

[Alan Johnson]

"Sequestering agents are not photographically inactive under all circumstances"-FDC p123.
Because Xtol concentrate is diluted 1+49 the ratio of sequestering agent concentration to phenidone and ascorbate concentration will be much higher than in Xtol if the same agent concentration is present in the working solution to prevent cloudiness.

 

[albada]

Distilled water is easier to get than most chelating agents, and quite cheap, too. Note, that your concentrate targets people who are very low volume developers, so the cost of distilled water should be irrelevant.

That cheap distilled water will eliminate cloudiness. That leaves the Fenton reaction. But the amount of iron will be low, sourced mainly from the sulfite and not from iron pipes, so Fenton's destruction of ascorbate shouldn't be an issue either. So I'm thinking I'll follow Alan's idea and say "if your tap water is hard, use distilled water" and ignore chelation because it won't be an issue for this one-shot brew.

Anyway...
While investigating chelation of iron, I noticed that your link to the table of stability contants shows that:

* Citric acid chelates Fe(III) well, and Fe(II) poorly.
* Salicylic acid chelates Fe(II) well and Fe(III) mediocrely (if that's a word).

Could both be used and get good chelation of all iron? These acids have the advantage of being widely available.

Mark Overton

 

[Rudeofus]

So I'm thinking I'll follow Alan's idea and say "if your tap water is hard, use distilled water" and ignore chelation because it won't be an issue for this one-shot brew.

If you still have space left in your instruction manual, you can add the line "and those whiners, for whom distilled water is completely unavailable for whatever obscure reasons, are encouraged to boil their hard tap water before using it to mix developer".

Boiling water drives out CO2, which in turn reduces the amount of HCO3- while leaving CO32-, which leads to precipitation of CaCO3, as frequently observed in water heaters of all kind.

* Citric acid chelates Fe(III) well, and Fe(II) poorly.
* Salicylic acid chelates Fe(II) well and Fe(III) mediocrely (if that's a word).

Could both be used and get good chelation of all iron? These acids have the advantage of being widely available.

If you look at the numbers, you'll see that Salicylic chelates FeII better than Citrate (6.55 vs. 3.2), and it also chelates FeIII better than Citrate (16.35 vs. 11.85). If you have Salicylic Acid in your dev, you won't need Citric Acid any more. Note that chelate stability does not tell the whole story since EDTA, which is a strong chelating agent for both FeII and FeIII, is known to accelerate the Fenton reaction.

Note that Salicylic Acid is not overly soluble (Wikipedia says 2g/l), so you may have to add some other acid anyway to get the pH you want. At 1g/l is is said to keep DS-10 stable, a developer you might remember

 

[Photo Engineer]

When you add salicylic acid to an alkaline solution, the solubility goes up! So, there may be some leeway here.

PE

 

[albada]

If you look at the numbers, you'll see that Salicylic chelates FeII better than Citrate (6.55 vs. 3.2), and it also chelates FeIII better than Citrate (16.35 vs. 11.85). If you have Salicylic Acid in your dev, you won't need Citric Acid any more. Note that chelate stability does not tell the whole story since EDTA, which is a strong chelating agent for both FeII and FeIII, is known to accelerate the Fenton reaction.

My goof! I swapped the FeII and FeIII numbers for Salicylic. So you're right; Salicylic beats Citric for both types of Fe ions.

I've heard before that EDTA accelerates the Fenton reaction, and that this is why Kodak uses DTPA in XTOL instead. But here's a report saying that DTPA also accelerates the Fenton reaction:

From http://www.efchemicalconsulting.co.uk/chelants-radical-damage.pdf
other aminocarboxylate chelating agents such as NTA
(nitrilotriacetic acid) and DTPA, in addition to EDTA,[7] all greatly accelerate the
Fenton reaction.​

My question is: Has anyone verified that EDTA indeed destroys ascorbate developers? Or is this a hypothesis based on studies not related to developers?

Mark Overton

 

[Dismayed]

Keep working! But for the time being I have a 2-year supply of XTOL tucked away.

 

[Rudeofus]

My question is: Has anyone verified that EDTA indeed destroys ascorbate developers? Or is this a hypothesis based on studies not related to developers?

A brief search revealed the following:

• EDTA slows down the Fenton reaction, but less so than other chelating agents. Note that in the experiments described in this paper, an Ascorbate solution lost 3% of its Ascorbate after 15 minutes in a phosphate buffer (pH = 7.0) "protected" by EDTA. Other chelating agents appeared to protect the Ascorbate much better, DETAPAC (which we commonly refer to as DTPA) is 10 times as effective at pH 7. Without chelating agent 30% of the Ascorbate was gone after 15 minutes!
• The same paper also claims that the effectiveness of a chelating agent is strongly dependent on pH. What this paper postulates for pH 7 is completely different in acidic environment, and may again be different at the pH of your dev. Note that DTPA gets better and better compared to EDTA at higher pH and that Xtol is known to be stable for about half a year.
• Another experiment discovered that EDTA becomes less effective after 24 hours in solution, strongly dependent on which other ions are in solution.

If you ask me, given these numbers, I would put a good iron chelating agent into your soup, at least during testing. Note that you pondered about much smaller changes in AA amount than 30% when you formulated and tested your dev, yet I do not think that you always tested your dev within 1 minute of mixing it.

PS: Please note that what I wrote above is no peer reviewed literature survey from an expert in the field, it's just an internet forum posting after a brief online search. Other papers I am unaware of may well state very different results and with my limited level of knowledge in the field I wouldn't be able to judge which one was right. So take these with a grain of salt, maybe more knowledgeable people in the forum could share their opinion on this.

 

[albada]

If you ask me, given these numbers, I would put a good iron chelating agent into your soup, at least during testing. Note that you pondered about much smaller changes in AA amount than 30% when you formulated and tested your dev, yet I do not think that you always tested your dev within 1 minute of mixing it.

I'll need to run some tests to see if Fe(II) and Fe(III) are a problem. It hasn't *appeared* to be an issue with my mix-to-use times of under an hour, but I won't know for certain until I've run tests. Do you know of an easy way to get a known molarity of these Fe ions in solution? Something better than a rusty nail? In addition, I have some salicylic acid, so I can run with/without tests to see how much difference that makes.

Your link shows that citric acid is good at sequestering Fe(III) but poor with Fe(II). So what else can be used for Fe(II)? How about histamine?

Mark Overton

EDIT: I still haven't seen any data showing that EDTA accelerates the Fenton reaction. I think I'll buy some and try it.

 

[Gerald C Koch]

Whether a particular chelating agent is useful in protecting ascorbate is rather complicated. It depends on the stability constant for a particular species like iron III but also on the redox potential of the complex. Ryuji did a lot of research on the net and recommentded that EDTA not be used. One of the problems he encountered was in finding all the redox potentials for chelating agents. The data is rather sparse. He settled on salicylic acid because it is readily available and cheap. BTW, the TEA is to complex any copper II which also catalyses the Fenton reaction.

As a source of Fe III ions may I suggest ferric ammonium sulfate and for iron II ferrous ammonium sulfate. Another posibility would be ferric nitrate. These salts are quite stable and can be obtained in high purity. Other ferric salts tend to decompose to various hydrated oxides in water. For the amounts needed for a test the ammonium ion will not be a problem.

 

[Rudeofus]

I'll need to run some tests to see if Fe(II) and Fe(III) are a problem. It hasn't *appeared* to be an issue with my mix-to-use times of under an hour, but I won't know for certain until I've run tests.

You are unlikely to see much effect since the activity vs. AA content curve is very flat in the region you are looking at. AA decay may explain some of your characteristic curve anomalies you described, though. If you look at Pat Gainer's data plot, 30% less AA is not a big issue as long as you are not concerned with 1/10 of a stop.

Do you know of an easy way to get a known molarity of these Fe ions in solution? Something better than a rusty nail? In addition, I have some salicylic acid, so I can run with/without tests to see how much difference that makes.

The electrical engineer in me would look at FeCl3 as source of FeIII, but chemists might know better. The trace quantities of FeIII you are going to add make it unlikely that the Cl- has any effect on your developer's properties.

Your link shows that citric acid is good at sequestering Fe(III) but poor with Fe(II). So what else can be used for Fe(II)? How about histamine?

You could still use DTPA like Xtol, or Dequest as suggested by PhotoEngineer ...

EDIT: I still haven't seen any data showing that EDTA accelerates the Fenton reaction. I think I'll buy some and try it.

From the second paper I linked to:

EDTA stored in buffer appears not only to lose to some degree its antioxidant potential (arising from chelation of traces of transition metal ions), but in some model systems even to acquire pro-oxidant activity.

 

[albada]

TEA vs METABORATE

Alan: Your statement that 99% TEA is difficult to obtain in the UK made me re-think the use of TEA. Another disadvantage of TEA is that because the pH-versus-temperature curve differs from metaborate, the developer can't use a fixed-factor of XTOL's times for temperatures above 20C. It would need its own time-temperature table. So I've decided to pursue the previous baseline dev based on sodium metaborate that I posted here: (there was a url link here which no longer exists)

The main purpose of TEA was to provide strong buffering in order to minimise the effect of inaccurate measurement of sulfite. A good solution is to measure sulfite by weight instead of volume. I mentioned earlier in this thread that electronic scales are cheap. One with .1g resolution is only US$10. That's the same cost as a packet of XTOL! At that price, there is no excuse for folks to not have a scale. Search for "scale .1g" or "scale .01g" in amazon.com.

I ran another strip on the metaborate-based baseline dev last evening, but adding propylene glycol as if it came from a concentrate (and boosting metaborate by .1g to adjust pH). The PG made the dev-time increase to 13.1 minutes (it was 12.25 without the PG), and the results look the same: a hair finer grain than XTOL. Here are scans from XTOL and this soup:

XTOL: , Test-soup:

FENTON

Rudi: The only question remaining is the rate of the Fenton reaction. One informal test I did a few weeks ago using the baseline dev above was: Develop a strip, let the soup sit for five hours, and dev a 2nd strip with the same soup. I got a 5% density-loss (on a log scale), whereas I expected about a 1% loss from using the dev twice. That 1% loss per hour is fine for a one-shot dev that is specified to be used within 30-45 minutes after mixing. But I need to test to see if much faster loss can occur. And as you point out, the AA-density curve is nearly flat there, so an X % density-loss means there was a much greater ascorbate-loss. So tests should be run in a steeper part of the curve. An AA/Phenidone ratio of 20 (instead of my 90) would be appropriate. The PC-Sulfite developer that I posted in January would work well for this testing.

Jerry: Thanks for the info about ferric and ferrous ammonium sulfate. I'll put them to use.

After all these months, I'm trying to finish this project. I've settled on that baseline developer. Now I need to insure that Fenton-destruction isn't a problem, and then run some tests on various kinds of film.

Mark Overton

 

[Gerald C Koch]

The electrical engineer in me would look at FeCl3 as source of FeIII, but chemists might know better. The trace quantities of FeIII you are going to add make it unlikely that the Cl- has any effect on your developer's properties.

Ferric chloride is a poor choice for making a solution of known ferric ion concentration. It is one of those compounds of indefinite composition. It hydrolyses in moist air and loses chlorine. It is also deliquescent. So there is no exact composition. The three compounds I suggested in a previous post are all stable and have definite compositions.

 

[albada]

Jerry mentioned that copper will catalyze the Fenton reaction also.
What form of copper would chemists recommend for getting a known concentration of Cu ions in solution?
Would copper sulfate be okay for this?

TIA,
Mark Overton

 

[Gerald C Koch]

Copper sulfate would be a good choice. It's cheap and readily available. The common name is blue stone

 

[Alan Johnson]

In the UK the maximum limit for copper in drinking water is 2mg/L and for iron 0.2mg/L.I don't know the US values.
http://dwi.defra.gov.uk/about/annual-report/2009/cir09thames.pdf
I daresay there may be high copper concentations in the UK which has mostly copper pipes and high iron concentrations in the US (which has mainly iron pipes?).

 

[Rudeofus]

In the UK the maximum limit for copper in drinking water is 2mg/L and for iron 0.2mg/L.I don't know the US values.

And what are the maximum limits of copper and iron impurities in the sodium sulfite used for mixing photochemistry?

 

[albada]

In the UK the maximum limit for copper in drinking water is 2mg/L and for iron 0.2mg/L.I don't know the US values.
http://dwi.defra.gov.uk/about/annual-report/2009/cir09thames.pdf
I daresay there may be high copper concentations in the UK which has mostly copper pipes and high iron concentrations in the US (which has mainly iron pipes?).

Alan, thanks for the info. I'll use your copper value of 2mg/L.

Regarding iron (and as Rudi hinted at above), it seems that more iron comes from impurities in the sodium sulfite than from tap-water. Spectrum Chemical's grades of sodium sulfite contain up to .001% iron, and their sodium metabisulfite contain up to .002% iron. In my developer, that's 0.9mg from the 45g of sulfite. I'll suppose I'll add 1mg of iron and 2mg of copper. Does anyone have more data about iron-content of sodium sulfite?

BTW, I did a leader-test last night from the baseline dev that had sat for 24 hours. Density was 2.6, whereas I would expect around 2.9. That tells me the Fenton reaction isn't overly fast using my chemicals in distilled water.

Mark Overton

 

[albada]

I haven't yet received my chemicals that will let me deliberately put Cu and Fe contaminants into the developer, but I did some tests to see how it currently holds up over 24-hours. I mixed the baseline developer in distilled water, with and without salicylic acid, and did leader tests when mixed, and after 24 hours. Here are the leader densities:

No salicylic, when mixed: 3.62
No salicylic, after 24 hrs: 3.65 (no loss)

With salicylic, when mixed: 3.67
With salicylic, after 24 hrs: 3.57 (small loss)

So salicylic acid made longevity worse? Huh?

Anyway, this shows that my chemicals (especially sulfite) are low enough in Cu and Fe that there's little or no perceptible loss of quality after one day. Maybe I should try this with our hard tap-water.

Mark Overton

 

[albada]

Interesting result: When developing a complete roll, you would expect a developer to develop less (make thinner neg's) than with a test-strip. That's because with a whole roll, there's much less developer present per square cm of film, so it gets more exhausted. So why did this happen with the baseline developer?:



With the roll, the developer became more active! It overdeveloped the roll, using the same time and temperature (and same pH). I'll guess that the by-products of the phenidone and AA accelerate development. I remember reading about this, but this is the first time I've seen it. I'll reduce development-time a little, unless somebody has a different idea...

Mark Overton

 

[Mr Bill]

Regarding iron (and as Rudi hinted at above), it seems that more iron comes from impurities in the sodium sulfite than from tap-water. Spectrum Chemical's grades of sodium sulfite contain up to .001% iron, and their sodium metabisulfite contain up to .002% iron. In my developer, that's 0.9mg from the 45g of sulfite. I'll suppose I'll add 1mg of iron and 2mg of copper. Does anyone have more data about iron-content of sodium sulfite?

Hi Mark, I no longer have any standards for photograde chemicals. At one time I did, and once or twice posted some data as examples. One I can still find is for potassium carbonate - not your chemical - but probably similar specs. This was from ANSI PH4.229-1987: Iron (Fe): 0.001% (m/m) max. So my guess is that the sulfite spec was the same, meaning that probably your supplier (Spectrum) meets a photograde spec for iron in sulfite. Probably. (Assuming carbonate and sulfite had the same spec for iron, and that the standard hasn't changed, and that I didn't mistype the original post.)

Regarding water, in general, my standard photo reference has always been a 1965 paper, Water Quality Criteria, by Lloyd West of Kodak. (The 1997 edition of IS&T's Handbook of Photographic Science and Engineering still used this paper as a reference.) Per West, in 1965 the US Drinking Water Standard was 0.3 ppm iron. He notes, "that level of iron can be expected to gradually produce stains and deposits on equipment and possibly photographic products." In a separate table of "Practical Limits for Common Impurities for Water," he lists 0.1 ppm for each of copper, iron, and manganese.

West only has a couple of paragraphs on iron, also saying "Iron is usually present in well water...especially in acid waters of pH less than 7. Sulfates of iron and aluminum are common sources of acidity of well waters."

Part of what West did was a survey of processing labs, and specs on their water. Today, you can likely find all of those water analyses on-line, searching for the city name and "water analysis," or "water quality report."

Hope this helps a bit.

 

[Rudeofus]

I'll guess that the by-products of the phenidone and AA accelerate development. I remember reading about this, but this is the first time I've seen it. I'll reduce development-time a little, unless somebody has a different idea...

Is there a chance that the oxidation products of Ascorbic Acid are not acidic and that the pH rises as more silver gets developed? This could at some point cause some AA to develop on its own, especially in the regions which have already seen some development (Silver == catalyst), and the curve would look like the one you got.

A pH measurement before and after development and comparing these for test clip and whole roll would likely shed some insight. You could also test if consecutive test clips souped with the same liquid show increasing contrast (and pH), so you wouldn't have to expend whole rolls on this.

If my suspicion proves correct, better buffering would help.