Why acid fix?

Discussion in 'B&W: Film, Paper, Chemistry' started by Ole, May 2, 2003.

  1. Ole

    Ole Moderator Staff Member

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    Leafing through a book from 1904, I came across the following interesting hint:

    "The addition of Sodium bisulfite to the fixer (plain hypo) is highly recommended. Not only will it increase the life of the fix, but it will also remove the unsightly brownish stain that sometimes occurs when using certain developers (notably pyrogallol)".

    Translation and rewording from German is entirely mine.

    Now my question is: Is this the reason nearly all commercial fixers are acidic? To REMOVE the Pyro stain??? Or does someone know differently?

    I fear this could be another of those weird traditions from the days of glass plates - like the standard sizes for printing papers...
     
  2. edbuffaloe

    edbuffaloe Member

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    I am no chemist, but I think photographers eventually figured out that fix didn't break down as fast when it was made acidic. The problem was that it didn't fix as quickly when adidified, which was resolved by increasing the concentration of thiosulfate. Highly concentrated sodium thiosulfate acidified with sodium bisulfite, potassium metabisulfite, or sodium sulfite and acetic acid produces a long-lasting fixer with high capacity and reasonable fixing times. I suspect that the acid plays a primary role in reducing stain from pyro (just as it does when you use an acid stop), but I don't think that is the main reason for acidifying fix.
     
  3. Thilo Schmid

    Thilo Schmid Member

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    Actually not all fixers are acid. The so-called "neutral" fixers are not only useful for keeping pyro stain, they also provide better climate in the darkroom. They are nearly odorless.

    The main reason why fixer usually is acid is to block remaining developer. Even if you use an acid stop, some developer might remain in the emulsion and might become active again in a basic solution. So fix should be at least neutral.
     
  4. Ole

    Ole Moderator Staff Member

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    </span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (tschmid @ May 2 2003, 04:28 AM)</td></tr><tr><td id='QUOTE'> The main reason why fixer usually is acid is to block remaining developer. Even if you use an acid stop, some developer might remain in the emulsion and might become active again in a basic solution. So fix should be at least neutral.

    Acid fix actually breaks down faster than alkaline; it's the sulfite that preserves, not the acidity. </td></tr></table><span class='postcolor'>
    This was not the reason given by E. Vogel in the 1904 book. Besides, the fixing process will effectively stop the development by removing the active silver halides: Monobath developers/fixers are very concentrated and extremely alkaline for this very reason. Unless the fixer is well past its usable life and the developer extremely concentrated, there will be no detectible development taking place in even the most alkaline fixers.
     
  5. Thilo Schmid

    Thilo Schmid Member

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    </span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (OleTj @ May 2 2003, 02:47 PM)</td></tr><tr><td id='QUOTE'>Besides, the fixing process will effectively stop the development by removing the active silver halides</td></tr></table><span class='postcolor'>
    Yes, of course. But it will take a while to process. Depending on the developer activity, another 30 seconds might not be negligible and may yield irreproducible results as the fixer wears.
     
  6. Ole

    Ole Moderator Staff Member

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    Slightly off topic, perhaps...

    Herr Vogel also recommends an acidic developer, based on iron (II) sulfate. "Plates developed in this solution have a beautiful blue colour". No mention of continued activity in acid fixer [​IMG]

    I'm tempted to try this stuff on RC paper - might be interesting?
     
  7. Robert

    Robert Member

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    My understanding

    1) Hardeners needed an acid enviroment to work.

    2) to protect against sloppy darkroom users.

    I wonder if the second one was more an issue with fiber paper then film?
     
  8. jansenh

    jansenh Member

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    </span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (Robert @ May 2 2003, 08:51 AM)</td></tr><tr><td id='QUOTE'>1) Hardeners needed an acid enviroment to work.
    </td></tr></table><span class='postcolor'>
    I have abandoned acid in my fiber process totally - after develop (Neutol 1+11) I stop with 3 minutes/4 changes water. Then two baths of plain-fixer (mr. Adams style no acid) - then a holding-tray with water a few minutes before Selenium 1:20. The whole cycle is performed in one single tray - with no acid in neither step.

    Am I missing something regarding hardeners here?
     
  9. Aggie

    Aggie Member

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  10. Donald Miller

    Donald Miller Member

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    The research that I have been exposed to indicates that the reason for acid (either in the stop bath or in the fixer) is for the purpose of halting developer action. The control of the length of time in developing is important to me but I do realize that others compensate in other ways. The addition of Sodium Sulfite to the Sodium Thiosulfate in the fixing bath is that the Thiosulfate in reaction with the silver halides produces free sulphur as one of the by-products. The sodium sufite combines with the free sulfphur to produce sodium thiosulfate. As I understand it this is a secondary part of the process and effectively lengthens fixer life. I don't have any experience with the alkaline fixers, I do understand that some pyro users use an alkaline fixer to limit stain reduction. I have, however, not found stain reduction to be problematic when using ABC Pyro in conjunction with Acetic acid stop and hypo.
     
  11. Donald Miller

    Donald Miller Member

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    Hardners are basically used only in the fixing baths of film (they harden the emulsion and reduce the chance for physical damage). In fact, the use of hardner in print baths will affect the toning ability of a print.
     
  12. Robert

    Robert Member

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    I think for modern films it isn't an issue. Maybe if your processing the film in warmer then normal temps then a hardner might help? I'm just using TF-2



    Sodium Thiosulfate 250 g
    Sodium Sulfite (anhy) 15 g
    Sodium Metaborate 10 g
    Distilled water to make 1000 ml

    Keeps fine. At least I end up dumping it and it's still fixing pieces of film.

    Which reminds me I need to make fix-))
     
  13. MikeK

    MikeK Member

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    I believe the use of an acid hardening fix was mainly used for films where the gelatin overcoats were very soft. In fact some old books recommended formalhyde to toughen the coat (as do some current E6 processes). Packaging I suspect is the main reason for an acid fixer being used for film and paper. I believe Kodak produces the only fixer (liquid) where you get two bottles, one with fixer and the other containing the hardening solution.

    I am a firm believer in the use of plain fix (Hypo and Bisulfite) for my prints and films or an Alkeline fix for film. Works just fine and eliminates chances of staining when toning.

    Mike
     
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  15. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member

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    Zonal Pro fixer also comes in two bottles, but unlike Rapid Fixer, you can buy them separately, so you don't need to pay for the hardener, if you don't want it. That was my regular fixer until I switched to TF-4.
     
  16. Ole

    Ole Moderator Staff Member

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    Hardening was also mentioned in the Vogel book, as something to be used "in very warm weather". It was a "standard" alun hardener.

    His film fix was plain hypo with sodium bisulfite, with hardener as an optional extra for those days when the emulsion wants to slide straight off the glass plate...


    If anyone wants recipes for vintage developers, I have them all...
     
  17. Donald Miller

    Donald Miller Member

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    OleTJ, Does your book contain a developer formula for 777? This is a developer that Ed Buffaloe has addressed on his web site.
     
  18. Robert

    Robert Member

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    Going back to the original question. Could it be for the smell? Sort of like if it smells it must work? I don't think my fixer smells at all. The lack of smell made me wonder if it was okay. I could see this being a marketing problem.
     
  19. fhovie

    fhovie Subscriber

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    I use TF-4 which, I understand is slightly basic. The struggle is -- do I get rid of the stop bath per the TF-4 instructions or do I keep the stop bath - per the paper instructions. I have opted to keep the stop bath but I only use it for a few seconds and add a water rinse before putting in the fixer. This keeps my fixer PH closer to where it should remain. I have ever had any problems either way with any kind of staining. I am just concerned about getting developer in the fixer. - Frank
     
  20. Donald Miller

    Donald Miller Member

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    As I understand the matter of the chemistry involved with TF4 is that if one uses an acidic stop bath between the alkaline developer and the alkaline fixer then it would appear that the greater danger exists in neutralizing the alkaline fixer. I believe that Formulary indicates using a water bath between the developer and TF4 fixer. The major benefit of using TF4 is in eliminating the possibility of stain reduction on the negative (in film processing when using pyro developers). Some have reported this stain reduction as taking place in an acidic environment. I do use pyro and I do use a stop bath with conventional hypo (thiosulfate and bisulfite) with no apparent deleterious effects. But then, I view general stain on the negative as counter productive in that it tends to reduce negative contrast. The stain that I view as beneficial is the stain that is proportional to the negative density and in the case of ABC is not visible in the same way that PMK is. I believe that the paper manufacturer is offering suggested processing procedures based upon conventional hypo usage. At least that is my interpertation of the matter.
     
  21. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member

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    For paper fixing with TF-4, I use a 30 sec. plain water rinse for RC paper and a 1 min. rinse for fiber based paper to prevent staining, which seems to happen with some developer/paper combinations and TF-4. An acid stop would neutralize TF-4.
     
  22. inthedark

    inthedark Member

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    </span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (dnmilikan @ May 2 2003, 09:58 AM)</td></tr><tr><td id='QUOTE'> Hardners are basically used only in the fixing baths of film (they harden the emulsion and reduce the chance for physical damage). In fact, the use of hardner in print baths will affect the toning ability of a print. </td></tr></table><span class='postcolor'>
    THANK YOU! This I needed to know. I shall begin to run two fixers for b&w, as my business splits about half and half paper and film. This explains a lot. I'm guessing that is also interferes with the ability of potassium ferrocyanide to effectively and controllably reduce and image?
     
  23. inthedark

    inthedark Member

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    </span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (MikeK @ May 2 2003, 05:42 PM)</td></tr><tr><td id='QUOTE'> I believe the use of an acid hardening fix was mainly used for films where the gelatin overcoats were very soft. In fact some old books recommended formalhyde to toughen the coat (as do some current E6 processes). Packaging I suspect is the main reason for an acid fixer being used for film and paper. I believe Kodak produces the only fixer (liquid) where you get two bottles, one with fixer and the other containing the hardening solution.

    I am a firm believer in the use of plain fix (Hypo and Bisulfite) for my prints and films or an Alkeline fix for film. Works just fine and eliminates chances of staining when toning.

    Mike </td></tr></table><span class='postcolor'>
    Agfa's professional line also comes with separate hardener, but I think the smallest quantity to purchase is a five gallon concentrate of fix.
     
  24. Robert

    Robert Member

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    I just wanted to add. When I made my new fixer up I did the usual test. The times for the old yellowed fixer was no longer then that of the fresh fixer. At least within my ability to time it. I haven't been using the old fixer for film in quite a while. Instead using it for just test prints. But it still seems to have had enough life. Well past the stated capacity and now turning yellowish. So it doesn't seem fixers need to be acidic to keep.
     
  25. inthedark

    inthedark Member

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    </span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (OleTj @ May 2 2003, 02:49 AM)</td></tr><tr><td id='QUOTE'> Leafing through a book from 1904, I came across the following interesting hint:

    &quot;The addition of Sodium bisulfite to the fixer (plain hypo) is highly recommended. Not only will it increase the life of the fix, but it will also remove the unsightly brownish stain that sometimes occurs when using certain developers (notably pyrogallol)&quot;.

    Translation and rewording from German is entirely mine.

    Now my question is: Is this the reason nearly all commercial fixers are acidic? To REMOVE the Pyro stain??? Or does someone know differently?

    I fear this could be another of those weird traditions from the days of glass plates - like the standard sizes for printing papers... </td></tr></table><span class='postcolor'>
    Well, I wonder if that is why I have five bottles of the stuff around the shop. I got only about 15 days of actual training and I keep coming across chemicals I have no idea what to do with. I just found out how to use potassium ferrocyanide about a month ago. I got about a pound and a half of it.

    What proportions did the book suggest. . .
     
  26. Donald Miller

    Donald Miller Member

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    It seems to me that the question that keeps coming forward is why the acidic nature of a fixer? The primary reason is to stop the alkaline action of the developing agent.

    For that matter when one reviews the PH of Sodium Thiosulfate, it is shown to have a PH of 11. That is certainly alkaline.

    When one reviews the PH of Sodium Sulfite it is shown to have a PH of 9.5. That is certainly alkaline as well.

    The formula for conventional Hypo fix is 32 oz of Sodium Thiosulfate and 4 Oz of Sodium Sulfite in one gallon of water.

    The formula for Kodak F6 fixer is 32 Oz of Sodium Thiosulfate, 2 Oz of Sodium Sulfite, 6 Oz of Acetic acid, 2oz of Kodalk (sodium metaborate--balanced alkali), 2 Oz of Alum to one gallon of water.

    The formula for Kodak F24 fixer is 32 Oz of Sodium Thiosulfate, one Oz of Sodium Sulfite, and 3 Oz of Sodium Bisulfite to one gallon of water.

    It would appear to me that the preponderance of the chemicals that make up the common fixers are certainly alkaline, with the possible exception of F6 and the acetic acid may be used to control the degree of alkalinity in that formula, rather then the formula itself being truly acidic.

    The reason for the addition of Sodium Sulfite (Na2 SO3), or Sodium Bisulfite (NaHSO3) is that in the chemical reaction that occurs in the removal of undeveloped silver halides (either Silver Chloride or Silver Bromide) from the film emulsion by Sodium Thiosulfate (Na2S2O3) one of the byproducts of that chemical reaction is free Sulphur (S). The free sulphur which is released then combines with the Sodium Sulfite or the Sodium Bisulfite (as the case may be). The result of this reattachment of the free sulphur is to form Sodium Thiosulfate (Na2S2O3). The net result of this chemical reaction is lengthening the effective life of the fixer solution. This chemical reaction will continue so long as there is either the Sodium Sulfite or the Sodium Bisulfite present in solution for the free sulphur to recombine with.

    While I certainly do not know the true chemical nature of all of the "brown stain"mentioned in the translated text, I certainly could believe that a portion and quite possibly a sizable portion of that stain may be the free sulphur which is a natural occuring by-product of this chemical reaction. The german text that you have translated would seem to bear out the result, consistant with the chemical reaction, of the addition of Sodium Bisulfite to the Sodium Thiosulfate in preparing a fixing bath.