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  1. #31
    Rudeofus's Avatar
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    Quote Originally Posted by Michael R 1974 View Post
    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.
    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.
    Trying to be the best of whatever I am, even if what I am is no good.

  2. #32
    Rafal Lukawiecki's Avatar
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    Quote Originally Posted by Rudeofus View Post
    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.
    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.

    Quote Originally Posted by Doremus Scudder View Post
    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.
    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.

    Quote Originally Posted by Gerald C Koch View Post
    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.
    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
    See rafal.net | Read rafal.net/articles

  3. #33

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    Quote Originally Posted by Rafal Lukawiecki View Post
    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?
    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.
    Last edited by Gerald C Koch; 03-21-2013 at 11:38 PM. Click to view previous post history.
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  4. #34
    Mainecoonmaniac's Avatar
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    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.
    "Photography, like surfing, is an infinite process, a constantly evolving exploration of life."
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  5. #35

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    Quote Originally Posted by Rafal Lukawiecki View Post
    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.
    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

  6. #36

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    Quote Originally Posted by Mainecoonmaniac View Post
    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.
    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

  7. #37
    Rudeofus's Avatar
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    Quote Originally Posted by Doremus Scudder View Post
    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.
    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 ...
    Trying to be the best of whatever I am, even if what I am is no good.

  8. #38

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    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.
    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.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

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  9. #39

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    Quote Originally Posted by Rudeofus View Post
    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 ...
    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

  10. #40

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    Quote Originally Posted by Doremus Scudder View Post
    ......................... 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
    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.

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