Alkaline fixer/wash times for FB paper

Discussion in 'B&W: Film, Paper, Chemistry' started by michael_r, May 8, 2013.

  1. michael_r

    michael_r Subscriber

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    I did a quick search and didn't really find anything so hopefully this thread isn't totally repetitive. An APUG member asked me a question about fixers recently and it reminded me of a subject I've wanted to discuss.

    Topic note: This concerns non-hardening, Ammonium Thiosulfate rapid fixers.

    We're told all things being equal, an alkaline fixer will wash out of paper significantly faster than an acidic one and that a hypo clearing agent isn't needed. Does anyone have hard data on this? I'm asking because based on what I think I understand from Haist I'm not convinced. However the chemistry is quite complex so I could easily be wrong.

    When a Potassium Alum hardener is included in a necessarily acidic fixer, it is true that a lower pH fixer is harder to wash out. I wonder if the notion alkaline fixers wash faster is an oversimplified extension of this (ie wash rates keep increasing as pH is elevated).

    1. The emulsion
    Given a non hardening Ammonium Thiosulfate fixer, my understanding is the most efficient washing will occur if the fixer pH is increased to the isoelectric point of the gelatin (~4.9), with no real benefits above that point. Am I wrong?

    2. The paper base
    My understanding is the rate of washing the thiosulfate and silver thiosulfate complexes out of the paper fibers, baryta etc. is essentially unrelated to the pH of the fixer. Am I wrong? This would also appear to contradict the hypo clearing non-requirement with alkaline fixers.

    If I'm reasonably correct about (1) and (2) above, faster paper washing would not be an advantage when using an alkaline fixer. The remaining benefits are no image bleaching with overfixing and possibly higher (?) capacity.

    Thoughts?
     
  2. Doremus Scudder

    Doremus Scudder Member

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    I've been thinking about this very issue lately as well.

    I'm hoping some of the fixer experts (PE, et al.) chime in here. I have doubts about the higher capacity claims as well. And, while we're at it, we might as well drag the Ilford archival sequence into the discussion. Lots of fodder here for an interesting thread. I'm looking forward to it.

    FWIW, I don't have an issue with washing longer, which I usually do, and I do residual hypo and silver tests (HT-2 and ST-1) to make sure my work-flow is not grossly out of whack, but I haven't taken the process to the limits in years, and certainly not with an alkaline fix like TF-4 or TF-5.

    Best,

    Doremus
     
  3. Mr Bill

    Mr Bill Member

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    Hi, I guess the lack of responses so far (Doremus aside) implies that there is not a wealth of information out there on this sort of thing. I don't have personal knowledge on this, nor any good tech papers, nor am I a chemist. My main experience has been with color neg/print paper, in very high-volume operations.

    Keeping in mind my limitations, my understanding is that with B&W materials the gelatin is the easiest part to wash. After this, there is some tendency for thiosulfate (and related) ions to adsorb to silver grains; I'm not sure how difficult or necessary it is to completely remove this. I take it that various wash aids might tend to bump off and replace this thiosulfate with their own ions. This is my own personal interpretation, not supported with hard literature references.

    Regarding the paper base (not RC paper), Mason, in Photographic Processing Chemistry (1966) says, "...the removal of further thiosulphate from the base is a lengthy process by washing alone. The reason for this retention is that the thiosulphate ions have to pass through the cell walls of the paper fibres, which are often protected by sizing materials, etc." There is no mention of pH in this respect, except mentioning that "washing is slowed down appreciably if an aluminium hardening fixing bath has been used." (we know that such a hardening fixer has a fairly low pH.)

    Mason mentions wash aids, saying, "The phenomenon was first fully investigated in 1956 by Crabtree, Henn, and King who showed that the introduction of a short soak in certain salt solutions between fixation and washing greatly increased the rate of the subsequent removal of thiosulphate and silver complexes." But again, pH is not mentioned.

    I don't know if there IS any modern research on this, other than occasional articles by photographers who have done their own tests for residual thiosulphate.

    To throw one further complication in there, about 10 years ago there where some internet articles to the general effect that it may be desirable to maintain some low level of residual thiosulfate - that is, to limit the washing. A couple of technical papers were referenced, of which I read one. It was regarding micro-film, where (per my fuzzy recollection) small "redox" spots tended to form on certain films, but not others. And that a tiny amount of residual thiosulfate and iodide existed in the unaffected films, but not in the others. (Don't put too much stock in my exact account of this.) I didn't investigate any further, as my day job didn't involve B&W by this time, only color, but you can probably find further info via a web search. My point is that it may be possible to over-wash.

    Perhaps someone will have some better information on the relation of fixer pH to washing. (I mean with some sort of solid basis other than "it's well-known," or that sort of thing.)
     
    Last edited by a moderator: May 9, 2013
  4. gzinsel

    gzinsel Member

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    I am hoping that some savvy chemists can answer these questions. Please!!!! How do you determine your fixer capacity. is there a way to determine? with some sort of "measuring system" when it is time to make new fix? Or does every one, like me, keep a tally sheet of "so many" 810's per liter, once you reach the suggested "limit", you then pitch it, and make new? I find this to be at best a guessing game, not archival, and at worst, wasteful. You are either using your fix "beyond" sound practice, or you not using it enough and throwing GOOD chemistry down the sink!!! I hate to guestimate!!!
     
  5. miha

    miha Member

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  6. michael_r

    michael_r Subscriber

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    Hi Doremus, Mr. Bill, thanks for the feedback so far. I have a few additional thoughts:

    1. When discussing ion exchange clearing baths as an aid to washing (HCA), Haist briefly mentions research pointing to the addition of clearing agents such as Sodium Sulfite, Sulfate and other compounds directly to the fixer, which could potentially eliminate the need for a separate HCA bath to improve washing/washing rates. At the time the book was written I guess there wasn't much on this yet, and it still concerned acidic fixers. Perhaps this is the "secret" behind purported faster washing with fixers like TF-4 or TF-5 rather than alkalinity per se (TF-5 is just slightly acidic). Perhaps people then incorrectly assume any alkaline fixer will wash out faster because TF-4 does.

    2. Haist mentions research and experiments that showed treatment of the print in an alkaline solution after fixation can help washing. However I find the section unclear. It seems to relate mostly to the emulsion and again deals with bringing the gelatin up to the isoelectric point. But it is not clear why it might help to raise the pH beyond the isoelectric point, nor are actual pH values discussed. Swelling is mentioned in reference to both the emulsion and the paper base, but it seems swelling can actually slow down the rate of washing the emulsion due to a longer diffusion path. It is not entirely clear to me what the conclusion is regarding the rate of washing the paper base. Swell seems to help, but swell vs what? Vs the state of the paper when it comes out of the acid fixer? Or vs a neutral state?

    3. Anchell makes the statement alkaline fixers wash faster than acidic ones. He doesn't really explain why other than to use laundry soap as an analogy, saying alkaline soap washed out of clothing fibers faster than an acidic detergent would. In Anchell/Troop the authors also cite faster washing as a benefit of alkaline fixers, although this is in relation to film, not paper (The Film Developing Cookbook).
     
  7. Mr Bill

    Mr Bill Member

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    Gzinsel, the general consensus is that you can use fixer until the silver content reaches some predetermined level. There are several sets of published recommendations for this; for commercial work a higher level is allowed, for maximum permanence a lower level.

    The problem is that it's difficult to know how much silver you've built up. This is why the general recommendation for counting the sheets. For a little better accuracy, you can purchase "silver-estimating papers." These are little test strips which you dip in the fixer, then compare the shade of the test paper to a reference; it gives you an approximate idea.

    If you're not already using a 2-stage fixer, you should look into this. It lets you get a lot more use out of your fixer, with a bigger safety margin to boot.
     
  8. Mr Bill

    Mr Bill Member

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    Don't forget that C-41 process uses a near-neutral (~pH 6.5) fixer, and it was introduced long before Haist's book. So I'm pretty sure the Kodak folks were well familiar with non-acidic fixers.

    Just about every common fixer (thiosulfate) contains a pretty fair amount of sulfite already, so I'm not sure how much would be needed to improve washing. I suspect it wouldn't be economical.

    I don't know anything about the fast-washing fixers, so no idea why.

    If Haist says research showed that, I'm sure it's legitimate. Too bad he didn't (or couldn't?) say more about it.

    I think that iso-electric points vary with the exact gelatin, so maybe it's wrong to give a certain pH value. Just guessing. If the main issue is the amount of emulsion swell, the solution makeup is probably more important than pH. Lloyd West of Kodak published a paper, "Water Quality Criteria" in 1965. He showed graphs of emulsion swell in various solutions, and by far the greatest amount of swell was in distilled water, more so than in a color developer.

    With modern materials, I'm not sure that they swell very much; I don't think so. There used to be special hi-temp fixers, etc, with a high salt content to limit swelling. But since modern color processes run at fairly high temp, you would guess that these are heavily pre-hardened. I'd guess that B&W emulsions are also, but again, this is guessing on my part.

    Yep, that argument doesn't carry much weight with me. Back when I was a kid, I would have ate that up, but having spent a good part of my adult working life working with various process systems and the like, I've heard a large amount of B-S. So in the real world, I always ask people, "how do you know that?", then "Are you sure?" To really confirm what they know, the "beer test" is used, ie., would you bet beer on that? For some reason, even though they would be glad to buy you a beer, nobody wants to risk losing one in a bet.
     
  9. michael_r

    michael_r Subscriber

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    I think I'll just stick with good old Ilford Rapid Fixer.
     
  10. Tom1956

    Tom1956 Inactive

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    My question would be: where is the point of diminishing returns on washing, and why would anyone want to leave the print with a softened gelatin when it was all done and dried? I've not been convinced that plain ordinary Kodak Fixer is still not the best way to go, and following Kodak's washing procedure. So far, prints I made 40 years ago are exactly as they were then. At that rate, it would have to be 200 years before they went sour.
    I chimed in because I am making a switch of all procedures toward 8x10 and FB printing. Thank you.
     
  11. Photo Engineer

    Photo Engineer Subscriber

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    This fixer describes TF-4 to a "T". To get that information, go to the Formulary web site and look up the instruction sheet for TF4. It has all kinds of information.

    PE
     
  12. Tom1956

    Tom1956 Inactive

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    Thank you. And not to steal the thread away from the OP, but I wonder how this fixer would allow safe ferrotyping with no hardener.
    http://stores.photoformulary.com/Detail.bok?category=ALL&no=148
     
  13. Photo Engineer

    Photo Engineer Subscriber

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    Easily, as today's papers are many times harder than older papers and so ferrotyping would only add to the gloss.

    PE
     
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  15. Rudeofus

    Rudeofus Subscriber

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    Note that neither Haist, nor probably the other authors were at liberty to disclose trade secrets, and alkaline fixers were once considered trade secrets. Haist does describe how F-6 improved on F-5 by raising pH just a notch to make archival washing possible while maintainung low pH for proper hardening. When Anchell and Troop write about alkaline fixers, you can assume they did the tests to make these claims, remember where the 'T' in Formulary's TF-4 and TF-5 comes from :wink:

    Generally it is hard to say how many sheets of paper one can process with a certain amount of fixer because not only does it depend on paper type, fixer dilution and stop bath carry over, it also depends on the amount of undeveloped silver in your images (think high key vs. low key image matter). You can fix a lot more AgCl than AgBr or AgI, so emulsion type (warm tone vs. cold tone) also makes a difference. If you have developer carry over, you might introduce potassium ions which supposedly have a detrimental effect on fixing. I would assume that published numbers on fixer capacity are conservative estimates that cover most cases of regular dark room work, and that retained silver tests are to be used by those who want to be 100% certain.

    And about Kodak color fixer with its pH of 6.5: the reason this pH is chosen is because dyes change their hue if pH is off, not necessarily because this pH is ideal for fixing.
     
  16. michael_r

    michael_r Subscriber

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    Regarding F-5/F-6, again, these are hardening Na Thiosulfate fixers. The type of hardener also makes a difference. Still, the discussion in Haist regarding fixer pH and washing (spread throughout the fixation and washing chapters) seems inconclusive. There are parts indicating the washing of gelatin is improved as fixer pH is raised to the isoelectric point (still acid), increasing fixer pH far above the isoelectric point of gelatin may actually retard gelatin washing, the rate of gelatin washing was not materially different for a chrome alum hardening fixer pH 3 and F-24, etc. Then there's the paper base with FB papers - the rate of paper washing is the same within a fixation pH range, the rate of paper washing is not materially affected by fixer pH, the rate of paper washing is improved with swelling when an alkaline bath is used after fixation, etc.

    Regarding Anchell/Troop, I would not assume anything actually. Absolutely no evidence is presented to support any of the voluminous conclusions the authors make regarding a myriad of materials and chemicals. There are also plenty of incorrect statements, and conclusions I don't agree with. Sorry but I can't take everything Troop says at face value, and there are clear biases in those books.

    Until I see credible test data, I remain unconvinced of the benefits (besides no bleaching) of alkaline Ammonium Thiosulfate fixers vs otherwise similar acidic fixers from Ilford or Kodak. There are also potential issues with alkaline fixers related to how development is stopped.
     
  17. Sal Santamaura

    Sal Santamaura Member

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    Such as?
     
  18. Rudeofus

    Rudeofus Subscriber

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    An alkaline fixer won't stop development ....
     
  19. michael_r

    michael_r Subscriber

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    Sal, for example if one only uses a water rinse in between developer and alkaline fixer, it needs to be quite thorough as development activity could restart in the fixer.

    Anyhow, my intention here is not to bash alkaline fixers so I apologize if any of it came off that way. I'm merely asking some questions. Statements have been made regarding the working properties of alkaline fixers vs acidic (non hardening) fixers in relation to certain tanning developers, wash times (film and paper), hypo clearing, the general desirability of all-alkaline processes, and fixing capacities. What do we really know? What is it based on?
     
  20. Rudeofus

    Rudeofus Subscriber

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    I believe that alkaline fixers swell gelatine faster and therefore allow faster fixation to archival standards. This means the paper needs to spend less time in fixer and therefore the paper base picks up less Thiosulfate which in turn helps during washing. Contrary to what you wrote multiple times I believe that gelatin is least swollen at its isoelectric point, therefore raising pH above that point would increase fixing and washing rate.
    Neither Anchell nor Troop ever developed an emulsion, therefore they may not be authorities in that regard. As much as the comments on T-grain emulsion and photographic emulsions may contain erroneous, opinionated or incorrect statements, I would consider his chapters on developers and fixers sound. If one sells fixer recipes to Formulary, he better be on top of this stuff as there is little room for snake oil in the analog market. Neither author owes us data charts or lab notes from when they tested and formulated fixers, and screaming "Their books are *&$ยง!" will rather drive them away from us (as it just so happens, Bill Troop hasn't been on APUG for ages) than make them give us their privately and at their own expense obtained data records.
     
  21. michael_r

    michael_r Subscriber

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    I didn't say the isoelectric point/pH had anything to do with gelatin swell. The discussion in Haist regarding the isoelectric point has to do with the affinity for thiosulfate and silver thiosulfate complexes.

    Swell is discussed from a diffusion perspective.

    With respect to The Film Developing Cookbook, it is a good book. I never said it was no good. But I can't agree everything they say about developers and fixers (developers in particular) is necessarily sound.
     
  22. Photo Engineer

    Photo Engineer Subscriber

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    Most products today are made with bone (ossein) gelatin from cows. The isoelectric point is about 4.5 and this is the point of minimum swell. So, the gelatin is "tight" in acid fixers and diffusion in and out of chemistry and salts is restricted. At an alkaline pH, gelatin is "looser" due to higher swell and thus chemistry diffuses inward and outward more easily. Fixing is faster.

    However, development can continue in an alkaline fix unless you either use a stop bath or a running water rinse.

    Ammonia odor can be a problem for some users of TF-4 and thus it was reformulated to remove the solids in the bottle and to prevent (or at least reduce) the ammonia odor. Thus we have TF_%>

    PE
     
  23. Rudeofus

    Rudeofus Subscriber

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    Michael, in your introductory post to this thread you wrote "Given a non hardening Ammonium Thiosulfate fixer, my understanding is the most efficient washing will occur if the fixer pH is increased to the isoelectric point of the gelatin (~4.9), with no real benefits above that point. Am I wrong?". There is no reason I am aware of why the isoelectric point should the optimal, quite to the contrary. Looking at Ron's chart tells me that pH 8 is quite good and sure enough that's what TF-4 is set to according to their MSDS. I have no idea how they avoid the Ammonia smell at this pH, though.
    It is more sound and better tested than most of the data or info I gather from forum or news group threads by a wide margin. Fact is that film development and fixation is a huge topic that occupied dozens of the brightest minds in the chemistry world, and few of their findings were ever made public. Many pieces of information published in the FDC were gathered informally and could not be publicly attributed to their sources, it is well known (ask Ron) how furiously Kodak defended and still defends their trade secrets from becoming public.

    Look at Mark Overton's heroic and ongoing effort in replicating Xtol to see how much work you can sink into one simple developer formula, and look at the sheer number of formulas in the FDC alone. It is quite plausible that Bill&Steve became so immersed in and overwhelmed by their effort that they drew some fast conclusions or let their opinion creep into their pile of accumulated facts. I still challenge everyone condemning the FDC and DCB to show me something better which is at least remotely up to date.
     
  24. nworth

    nworth Subscriber

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    It's surprising how little information there is about washing papers. The reason may be the complexity of the issue. The paper, the fixer composition, the fixing time, the temperature, the washing apparatus, the pH, and a host of other things are all involved. Mees and James has a short section which is reasonably informative. Important factors they mention include: 1. Fix no longer than 10 minutes; 2. Keep the pH above the isoelectric point to retard absorption by the gelatine; 3. Use a high turbulence, minimum water washer that maintains fresh water across the print; 4. Ammonium thiosulfate fixers wash out faster than sodium thiosulfate; 5. Hardeners retard washing; 6. Salt treatments, like HCA, can reduce washing times; 7. Paper is a lot harder to wash than film.

    Ref: C. E. K. Mees and T. H. James, "Modern Photographic Process" Macmillan, 1966. pp 403-405.
     
  25. michael_r

    michael_r Subscriber

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    Rudeofus, I'll try to clarify a few things and give some more examples from the text to show why I am confused.

    Regarding the isoelectric point, again this was not about swell. The question I was asking is - is there a benefit in terms of washing the gelatin at pH values above the isoelectric point? I'm basing this on Haist pp. 634-635 (Volume 1). As the pH is increased to the isoelectric point of the gelatin, the gelatin becomes less positively charged and thus has less of an attraction for negatively charged thiosulfate and silver thiosulfate ions. At the isoelectric point, the gelatin molecules are neutral and thiosulfate is not retained. The wording is slightly vague as to whether there should be any improvement in washing as the pH is increased further and the gelatin molecules become negatively charged. But then the results of Crabtree, Eaton and Muehler are presented. Those results appear to support the notion it doesn't help to go higher than the isoelectric point unless Potassium Alum specifically is used as a hardener. "...the effect of pH of the fixing bath is of primary importance when the bath contains potassium alum." This concerns the gelatin. Regarding prints and the pH of the fixing bath: "...the rate of washing differed only during the very first minutes, after which the rate was the same regardless of the composition of the fixing bath. The washing of photographic prints involves other factors that influence the removal of thiosulfates from the photographic material." Note this concerns fresh fixing baths. things get more complicated with exhausted baths.

    Under the topic of two-bath fixation there are some interesting comments. On p. 640 there is some discussion regarding the difficulty of removing thiosulfates and silver thiosulfates from the paper base of a print vs the emulsion. "Fixing baths with pH values above or below the isoelectric point of gelatin have little or no effect upon the retention of thiosulfate or silver thiosulfates by photographic prints when the retained thiosulfates are in the paper base or baryta layer." Later in that section on p. 642 - again in reference to Crabtree, Eaton, Muehler: "pH values in the range of 4.0 to 5.6 had little effect on the rate of removal of hypo and silver"

    In the section on washing on p. 665 there is an interesting comment: "Any treatment that causes the emulsion layer of film or plates to swell increases the diffusion path within the emulsion and may retard slightly the washing of the emulsion free of thiosulfates or other salts. The same treatment, however, would be beneficial to the washing of paper prints. The paper emulsion layer would swell and impede slightly the washing of the emulsion layer, but most of the washing time is concerned with the elimination of the thiosulfate from the rest (baryta layer or paper base) of the paper print. A treatment, such as with an alkaline solution, that causes the paper fibers to hydrate and swell, or to rupture the paper sizing, will leave the paper fiber surfaces and channels more accessible to washing by water."

    Earlier, alkaline bath treatments are discussed, but again mostly in reference to the thiosulfate and silver thiosulfate ions bound by aluminum-gelatin complexes (ie fixed in a potassium alum fixers).

    It should be noted this all seems to concern sodium thiosulfate fixers, not ammonium thiosulfate rapid fixers, which could be pretty important.

    Anyhow hopefully the above gives a better idea of why I find this a little unclear. Perhaps some testing of a few alkaline rapid fixers vs acidic ones would help. By testing for retained hypo, perhaps some quality data on relative washing times could be obtained.
     
  26. Photo Engineer

    Photo Engineer Subscriber

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    Mason gives a very good description of washing, including the differential equation that shows how it takes place. Haist shows the effects of pH on washing and I have shown the effects of pH on swell both here and in my book. Swell is maximized at pH 9 and minimized at pH 4.5. Washing and fixing are best at pH 9 and worst at pH 4.5. Kodak sold fixers that worked at both pH values. At these different swell values, the fixers must be totally different in order to contain hardeners.

    Michael has it backwards wrt pH vs swell and fix and wash rate.

    Anchell and Troop is much more thoroughly researched compared to Anchell. Bill Troop actually talked to Grant Haist to confirm many of the statements in A&T. The soap analogy by Anchell is reasonable but not entirely accurate.

    PE