How Does Sodium Sulfite Wash-Aid Increase Fixer Capacity?

I think what Rafal wants to investigate is whether sodium sulfite will do some of the actual fixing on its own, thus making the wash-aid bath a kind of "mini" second fix. I believe he wants to single-bath fix and count on the wash-aid to take up some of the slack when the single fixing bath becomes exhausted. I.e., I believe he wants to use the fixer past its "for optimum permanence" limit and rely on the wash aid to get the print to "optimum."

There are some references (Ilford data sheets, etc.) that mention that fixing bath capacity can be "increased" by using a wash aid.

I would tend to be skeptical of relying on sulfite as part of the actual fixing process. First, the effect, if it exists at all, must be rather weak. Second, there is no way that I know of, nor any literature about, determining the capacity for a fixing bath using sulfite vs. not. Third, since fixer is much better at fixing than sulfite (if the sulfite does anything at all), it is simply easier and more secure to use the fixer to do the job and replace it as needed.

Single-bath fixing and optimum permanence means discarding the fixer relatively often in order to keep the dissolved silver under the limit for optimum permanence. Two-bath fixing allows much more capacity (approx. 4x) while at the same time ensuring that optimum permanence is achieved. Why substitute a proven procedure for a questionable and experimental one? Just to not have to make room for another tray? Or to save a couple seconds setting up and pouring in the chemicals?

A wash-aid has been shown to help in the washing process, especially for fiber-base papers, but it has not ever been in the mainstream as a fixer. There must be a reason for this; I'm sure Haist, Mees and many others would have recommended sodium sulfite for this purpose if it had been practical. I tend to conclude, therefore, that it is not.

Best,

Doremus


www.DoremusScudder.com

You know I never noticed the bath itself to be milky, just at certain times of the year the prints would exhibit a white scum after washing.

thanks for your concise explanation.

Rudeofus said:

Instead of Sodium Metabisulfite and Hexametaphosphate one can simply add Citric Acid to the milky clearing bath. Not only does it form a nice buffer with Sulfite between pH 6 and 8, the Citric Acid also works as chelating agent for all these ions which tend to form white scum with Sulfite or Carbonate, and it dissolves easily in water.

Instructions for making such a mix are very simple:

• Prepare working solution of hypo clearing agent with Sodium Sulfite, Sodium Carbonate (or whatever your recipe says) and tap water.
• The mix will be milky depending on your water hardness. Now add Citric Acid (anhydrous, monohydrate, it doesn't matter) until the working solution clears. Don't add too much Citric Acid or your bath will smell from SO2. If it does, add Sulfite or Carbonate to raise pH back to where it doesn't smell.
• Done!

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Thank you Gerald. I do mix the sodium Hexametophospahte hot by itself but it immediately clumps together eventually it dissolves

I will give your formula go and once again appreciate your advice.

Gerald C Koch said:

Whether the silver complexes are adsorbed in the emulsion or trapped in the the paper fibers is really immaterial in a practical sense.

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It might be important because the remedy could well be different. The emulsion responds to alkalis with swelling, which improves washing, while AFAIK paper base doesn't care all that much about pH. I would therefore assume that Carbonate based hypo clearing bathes work for film and RC paper while I don't expect them to be very beneficial for washing FB prints.

When we discuss Silver Thiosulfate complexes we need to understand that there are two possible ways how they stick to fibers: it might be the Thiosulfate which somehow binds to the fiber, but I would rather suspect the Silver ion accepting some reactive group as another ligand.

Michael R 1974 said:

If this is indeed what Rafal is looking for, not likely to work very well. Haist briefly discusses Sodium Sulfite under "other fixing agents". As we know from film developers, Sodium Sulfite is a silver halide solvent, but it is a weak one.

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There are different challenges for fixing bath 1 and fixing bath 2. Fixing bath 1 should remove the bulk of the Silver Halide which means you need something that can bind a few g/l of Silver ion. Sulfite certainly won't do that, especially in the presence of matching amounts of Bromide or Iodide.

Fixing bath 2, on the other side, neither has much Silver to deal with nor much Bromide/Iodide to compete against, so the numbers look much more favorable for a weak Silver solvent that washes out easily.

Rudeofus said:

There are different challenges for fixing bath 1 and fixing bath 2. Fixing bath 1 should remove the bulk of the Silver Halide which means you need something that can bind a few g/l of Silver ion. Sulfite certainly won't do that, especially in the presence of matching amounts of Bromide or Iodide.

Fixing bath 2, on the other side, neither has much Silver to deal with nor much Bromide/Iodide to compete against, so the numbers look much more favorable for a weak Silver solvent that washes out easily.

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Rudi, this is precisely what I am thinking, you have managed to express my understanding of the function of fix bath 1 and bath 2 very well.

Doremus Scudder said:

I think what Rafal wants to investigate is whether sodium sulfite will do some of the actual fixing on its own, thus making the wash-aid bath a kind of "mini" second fix. I believe he wants to single-bath fix and count on the wash-aid to take up some of the slack when the single fixing bath becomes exhausted. I.e., I believe he wants to use the fixer past its "for optimum permanence" limit and rely on the wash aid to get the print to "optimum."


There are some references (Ilford data sheets, etc.) that mention that fixing bath capacity can be "increased" by using a wash aid.


I would tend to be skeptical of relying on sulfite as part of the actual fixing process. First, the effect, if it exists at all, must be rather weak.

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Doremus, I think you understand some of my goals, indeed, I would like to know if a good, potent sodium sulfite wash aid can function as fix 2—but definitely not as fix 1, which we know, it cannot do. Because the functions of the two baths are quite different, my hypothesis is that it might be able to. However, I do not wish to exceed fix 1 capacity beyond—this is important!—2g/l, which is about 40 sheets of 8x10 per 1 l, which is the same as capacity of a normal fix 1, before you would rotate it out based on Kodak and Ilford recommendations. However, the best part is, based on the Ilford and Digital Truth references, which I quoted above, that capacity of fix 1 is exactly what they are recommending for archival/optimum process when a wash-aid is used. The two approaches seem to have identical capacities.

In other words: classical 2 bath fixing gives you 4x capacity of fix 1 compared to a single bath. Single bath fixing using alkaline or neutral fxer, with a wash aid, gives you 4x capacity of fix 1 compared to a single bath. So what is the saving? Twofold: you would do the wash aid anyway, so one step can be eliminated. Secondly, in 2 bath fixing, every four rotations you must throw away the 2nd fix, instead of promoting it to 1, due to the carry-over buildup of iodide and other pollutants, according to Kodak. So, if this works (and that is what I am trying to get to grips with) then this is a very considerable saving to the environment, not to mention our time. Also, avoiding a 2nd fix, means even less thiosulfate in the paper fibres etc, as we cut the contact time to a half.

Gerald C Koch said:

Whether the silver complexes are adsorbed in the emulsion or trapped in the the paper fibers is really immaterial in a practical sense. What is important is the kinetics of the process. The silver complexes in film and RC papers are removed much more quickly with washing than those in FB papers. So what controls the rate of silver removal in FB papers is absorption on the paper base. In any set of kinetic reactions it is the slowest reaction which determines the overall speed.

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Gerald, thank you for your patient explanations, which I think I follow now. Just to see if I understood you, may I ask you how can we be sure that the slowest reaction is, indeed, that of removal of thiosulfate from paper base, if the duration of the immersion of paper in the fixer can be cut significantly, such as when using Ilford approach of film-strength ammonium thio fixer for 1 minute, or an alkaline/neutral rapid fixer, 12% (film strength) that references say washes out much more easily than the sodium thio? Secondly, am I right to think that you assume that one must use another fixer bath to speed up the removal of thio and silver-thio compounds? If a hypothetical compound X could remove those, would it not be better to rely on that, as there would be no additional thiosulfate entering fibres while desorbing the complexes?

Thank you, everyone, for humouring me with your explanations and your patience, which I am very grateful for.

Rafal Lukawiecki said:

Gerald, thank you for your patient explanations, which I think I follow now. Just to see if I understood you, may I ask you how can we be sure that the slowest reaction is, indeed, that of removal of thiosulfate from paper base, if the duration of the immersion of paper in the fixer can be cut significantly, such as when using Ilford approach of film-strength ammonium thio fixer for 1 minute, or an alkaline/neutral rapid fixer, 12% (film strength) that references say washes out much more easily than the sodium thio? Secondly, am I right to think that you assume that one must use another fixer bath to speed up the removal of thio and silver-thio compounds? If a hypothetical compound X could remove those, would it not be better to rely on that, as there would be no additional thiosulfate entering fibres while desorbing the complexes?

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It is easily shown that thiosulfate in RC papers is washed out faster than in FB papers when using the standard fixing method. This can be done by using HT-1a for each of the two papers and noting the amount of discoloration in the test solution.

The idea behind the Ilford method of short fixing times with FB papers is to prevent the fixer from entering into the fiber base. Therefore the slow removal from the paper is avoided. Ammonium thhiosulfate removes silver halide faster than does the sodium salt. It also washes out faster than sodium salt. This allows the Ilford method to use a higher concentration of ammonium thiosulfate than is normally used.

As you probably know the theory behind a two bath fixing system is that the amount of silver in the second bath never reaches the concentration that exists in a single bath fixer. Most of the silver is removed by the first bath. Therefore the second bath always contains significantly less silver than the first one. When the fixing rate of the first bath slows the second bath replaces the first one. A new fresh bath then replaces the older second one. The two bath method works for either sodium thiosulfate or for ammonium thiosulfate.

The actual rate of removal of thiosulfate during washing is constant whether a single bath or two bath system is used. This is based on the same composition of the fixer in all the baths. What is different is that the two bath system insures that the concentration of silver-thiosulfate complex is lower in the second bath. Therefore the reduction of the complex in the paper is easier to attain. Once again it is important to understand that there are two processes going on during the wash. The removal of thiosulfate and the removal of the silver-thiosulfate complex.

There are better compounds to use as fixing agents than thiosulfate. Haist mentions several in his book "The Monobath Manual." However they are all more expensive and/or harder to obtain than thiosulfate. Which explains their use being limited to monobaths.

Thank YOu for asking some very well thought out questions. Once again the fixing process is all about kinetics. The use of a washing aid only effects the speed of removal but not the final result.

Can I just use sodium sulfite as a wash aid? I have over a pound of the stuff left over when I used it to clear Polaroid type 55 negs.

Rafal Lukawiecki said:

Doremus, I think you understand some of my goals, indeed, I would like to know if a good, potent sodium sulfite wash aid can function as fix 2—but definitely not as fix 1, ... However, I do not wish to exceed fix 1 capacity beyond—this is important!—2g/l, which is about 40 sheets of 8x10 per 1 l, which is the same as capacity of a normal fix 1, before you would rotate it out based on Kodak and Ilford recommendations. However, the best part is, based on the Ilford and Digital Truth references, which I quoted above, that capacity of fix 1 is exactly what they are recommending for archival/optimum process when a wash-aid is used. The two approaches seem to have identical capacities.

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Rafal,

I would be skeptical of this too. Let's look at single-bath fixing without a wash aid: Ilford and others give a limit of 2g/l of dissolved silver compounds for a "commercial" or "general purpose" level of permanence. For "optimum permanence" a much lower level of 0.5g/l of silver in solution is given, which reduces the capacity of the single fixing bath to about 10 8x10s per liter.

If you want this level of permanence (and any exhibiting photographer should strive for this IMO), then you should toss a single fixing bath after a rather small throughput. Adding a sodium sulfite/wash aid to this single-fixing bath is simply not going to increase the capacity by 4x. From what we've been discussing, it may (emphasis on the "may") increase the fixer capacity a small amount, maybe even 10%, but likely less. This would allow you one extra 8x10 from your single fixing bath. You would have to test print 11, and 12, 13 ... if you really want to find the limit of this method every time for many runs to come up with some kind of empirical idea of what the capacity of single-bath fix plus wash-aid bath as fixer (or even a more concentrated sulfite bath) was. As I've mentioned before, this has likely been done by the chemists at Kodak already. If it were a promising path, I believe it would have been explored more already. Since it hasn't, I would tentatively conclude that it's simply not worth it to use a sodium sulfite bath as a "fixer extender" or a second fixing bath.

With two-bath fixing, as Gerald so adroitly points out, you have, in essence, a fresh fixing bath in bath 2, which should never reach even the 0.5g/l level of dissolved silver if used correctly. This reliably ensures that complex argentothiosulfate compounds are reduced to more soluble ones which will wash out. Easy, proven, reliable and you don't have to do any time-consuming tests.

Whatever method of fixing you finally decide on, just make sure not to exceed the capacity and test often. I test the last print of my fixer run for residual thiosulfates and residual silver each toning session.

Best,

Doremus

Mainecoonmaniac said:

Can I just use sodium sulfite as a wash aid? I have over a pound of the stuff left over when I used it to clear Polaroid type 55 negs.

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Yes, see earlier posts in this thread for some formulas.

Since the amounts are not all that critical, I often mix my wash-aid as a spoon recipe: one Tablespoon of sodium sulfite per liter with a generous pinch of sodium bisulfite as buffer. Use one-shot.

Using only sulfite is possible, but not quite as effective and the capacity is reduced somewhat. See the discussion earlier in this thread as well.

Best,

Doremus

www.DoremusScudder.com

Doremus Scudder said:

Adding a sodium sulfite/wash aid to this single-fixing bath is simply not going to increase the capacity by 4x. From what we've been discussing, it may (emphasis on the "may") increase the fixer capacity a small amount, maybe even 10%, but likely less.

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You say it doesn't, yet Ilford claims it does ... and I would assume that Ilford did some serious testing before they published their numbers. Did you?

Note that Ilford would love to sell us more fixer concentrate ...

Can I just use sodium sulfite as a wash aid? I have over a pound of the stuff left over when I used it to clear Polaroid type 55 negs.

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Using a plain sodium sulfite bath as a wash aid may cause a problem with hard water. A scum of calcium sulfite may form on prints and film. It would be best to include 5 g/l of a chelating agent such as EDTA or Calgon in the bath.

Rudeofus said:

You say it doesn't, yet Ilford claims it does ... and I would assume that Ilford did some serious testing before they published their numbers. Did you? Note that Ilford would love to sell us more fixer concentrate ...

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Rudeofus,

No, I haven't done serious testing and, if you read my posts carefully, you'll see that I've left the possibility open.

However, the claim that Rafal refers to and that you reference above is found ONLY in the Ilford data sheet on processing black-and-white materials ( http://www.ilfordphoto.com/Webfiles/200621111117720.pdf ). Such a claim is NOT found in either the data sheet for Ilford Rapid Fix or Ilford Hypam.

What does appear in these two documents, however, is the differentiation between "commercial" and "optimum" levels of permanence. The references to Washaid in these data sheets only states that its use will speed washing. No mention of extended fixer capacity. I don't know who wrote which documents, but, to me, the B&W processing document seems simplified and directed at beginners. No mention is made of dissolved silver content in the fixer, nor of different levels of permanence. I would tend to think that the reference to extended fixer capacity is either an error due to editing or refers to "commercial" levels of permanence. I have never seen any reference to extended fixer capacity from Kodak, whose research I trust much more than Ilford's.

My point to Rafal is simply that two-bath fixing is proven and using sulfite to extend fixer capacity is iffy at best and would require testing (as you point out). I would think that simply using two-bath fixing would be a lot more secure if one were just interested in making prints.

On the other hand, if one is primarily interested in exploring photochemistry and, specifically, the ability of sodium sulfite to extend fixer capacity, then, have at it! I make prints for exhibition. I'm not that interested in expanding the database of photochemistry. I'll stick with the tried and true processes explored and documented extensively by those that have a lot more knowledge and experience than I ever will in photochemistry.

Best,

Doremus


www.DoremusScudder.com

Doremus Scudder said:

......................... I'll stick with the tried and true processes explored and documented extensively by those that have a lot more knowledge and experience than I ever will in photochemistry.

Best,

Doremus


www.DoremusScudder.com

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And a sodium sulphite rinse, with maybe a pinch of metabisulphite and citric acid is very cheap and known to work. The downside is yet another tray or two which I would not be able to fit in my tiny darkroom. My solution to this latter problem which was expensive but convenient was to get an extra two-slot Nova processor.

john_s said:

And a sodium sulphite rinse, with maybe a pinch of metabisulphite and citric acid is very cheap and known to work.

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It is well established that hypo clearing bath helps in washing out Thiosulfate (and possibly its insoluble Silver complexes), but what Doremus understandably challenges is something different: that a wash step in hypo clearing agent after fixing allows a single bath fixer setup to process as many sheets as normally a two bath fixer setup.

I guess we are at the point that only testing will help reject the null hypothesis.

I'll try to devise a test, and hopefully, run it, but it'll have to wait till I'm back from my upcoming US trips. Late April or even May... I want to run the tests on what some here called an "exhausted" fixer, or which I think is at the borderline, 2g/l, accumulated through a normal use.

Rafal Lukawiecki said:

I guess we are at the point that only testing will help reject the null hypothesis.

I'll try to devise a test, and hopefully, run it, but it'll have to wait till I'm back from my upcoming US trips. Late April or even May... I want to run the tests on what some here called an "exhausted" fixer, or which I think is at the borderline, 2g/l, accumulated through a normal use.

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I imagine the test should be fairly straghtforward. Simply fix a prints in a single fixing bath, do not use a wash aid, wash them thoroughly (overkill here to be sure) and subsequently test them sequentially for residual silver with ST-1. (I know ST-1 test doesn't really give quantifiable results, but it should work for comparison purposes). To really be accurate, you should fix unexposed paper of the same type and size. Unusably expired paper would be ideal for this if one had, or could get it. You should also fix for the same time

Then, simply note how many prints go through the fix and wash until the stain appears. Now, repeat the experiment adding the wash aid. See if the number of prints that go through the process before the telltale stain appears is significantly more.

To keep from using lots of unexposed paper, one could use 250ml of Ilford Rapid Fixer in an 8x10 tray, which would, if using paper with developed silver images on it, have a capacity (using Ilford's numbers) of 10 8x10 at a "commercial" level of permanence and 2.5 8x10 at the "optimum permanence" level. However, since undeveloped paper is being used, and there is no image silver formed, the capacity should be significantly less due to the increased amount of undeveloped halides, maybe even less than 50% of the throughput recommendation.

I don't know how sensitive ST-1 is, so each print from beginning to end should be numbered and tested, stopping when a few prints show increasing levels of stain from the ST-1 test.

The level of permanence when the stain appears is irrelevant to the experiment; just use the number of prints made before the stain appears as a basis for comparison. If a wash aid really can increase a fixer's capacity by 4x, then one should be prepared to fix four times the sheets used in the first part of the experiment during the second. (I still cannot see how this would be possible...)

If the wash-aid increases capacity by a lesser amount, that should be apparent as well.

Best,

Doremus

Note that fixing has more variables than just the amount of chemistry that's in the bath: agitation, paper type, emulsion type, ambient temperature, freshness of fixer, ... getting reproducible numbers might be quite a challenge unless one creates very reproducible start conditions. This could also mean that in some instances we could fix much beyond the (most likely conservative) numbers given by Ilford.

If you want to do reproducible tests I'd say you prepare AgCl and AgBr (from AgNO3 + KCl/KBr + filtration + drying) and season the fixer with predetermined amounts of AgCl/AgBr. You don't need to prepare much seasoned fixer as you can test fixation and washing with small test clips. This test setup allows to to quickly determine how much Silver can remain in fixer for archival fixing with various fixing and washing techniques.

Once you have these numbers, all you have to do is translate these back to your practical printing setup.

Doremus Scudder said:

No, I haven't done serious testing and, if you read my posts carefully, you'll see that I've left the possibility open.

However, the claim that Rafal refers to and that you reference above is found ONLY in the Ilford data sheet on processing black-and-white materials ( http://www.ilfordphoto.com/Webfiles/200621111117720.pdf ). Such a claim is NOT found in either the data sheet for Ilford Rapid Fix or Ilford Hypam.

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Because this issue is central to this thread, I contacted Simon Galley and asked him whether the information in this data sheet is still valid, i.e. whether use of a hypo clearing bath indeed allows four times higher reuse of single bath fixer. Here is his response (reposted with his explicit permission):

Simon R Galley said:

Our technical service stand by the statements, they have been verified and checked over many years.

Simon ILFORD Photo / HARMAN technology Limited

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I have just stumbled on one more reference which suggests that using hypo clearing agents extends archival capacity of the fixer from its, otherwise, measly equivalent of 10 8x10" sheets per 1 l. In Tim Rudman's "Toning Book" (2010, ISBN 1-902538-23-4) on page 156, chapter "Archival permanence", section "Hypo-Clearing Agents", 5th paragraph reads:

Hi Rafal, I can't see how this is possible. Is hypo able to dissolve Ag(S2O3)- ?

Rudeofus said:

IIRC there were published tests of the individual hypo clearing agents, and that Sodium Sulfite was deemed the best. What one will eventually use probably depends on availability and cost as much as on actual performance.

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I wonder if it were a benefit to use a mixture of different salts,totalling a 2%solution
:confused:

Tetenal sells test stripsto measure silver content.for me they worked far better than an iodide test solution

Does Rudman provide any scientific proof for his pronouncement?

Gerald C Koch said:

Does Rudman provide any scientific proof for his pronouncement?

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Perhaps he is accepting Ilford's statement, which seems a reasonable thing to do.

Personally, I choose to use 2-bath fixing, made easier by having the fixer sitting permanently in a Nova vertical slot unit.