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Thread: Why acid fix?

  1. #21

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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&#33; 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&#39;m guessing that is also interferes with the ability of potassium ferrocyanide to effectively and controllably reduce and image?
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  2. #22

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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&#39;s professional line also comes with separate hardener, but I think the smallest quantity to purchase is a five gallon concentrate of fix.
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  3. #23

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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&#39;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&#39;t seem fixers need to be acidic to keep.

  4. #24

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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. . .
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  5. #25

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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.
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  6. #26

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    </span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (Darkroom ChromaCrafts @ May 6 2003, 06:09 PM)</td></tr><tr><td id='QUOTE'> </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. . . </td></tr></table><span class='postcolor'>
    If you&#39;re using commerically prepared fixer I doubt you need to worry. I think you&#39;re asking about the sodium bisulfite? Most commerical chemicals aren&#39;t likely to be improved by adding things.

    For the unknown chemicals you could try Jack&#39;s chemical website:

    http://www.jackspcs.com/chemdesc.htm

    Also you might want to look at:

    The Darkroom Cookbook by Anchell and Troop.

    But unless you&#39;re mixing your own chemicals up I don&#39;t know if you really need to.

  7. #27
    Ole
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    </span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (dnmilikan @ May 6 2003, 03:04 PM)</td></tr><tr><td id='QUOTE'> 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.
    </td></tr></table><span class='postcolor'>
    According to my MSDS, Sodium Thiosulfate solution has a pH of 6.0 to 8.5 - not alkaline at all&#33;

    Sodium Metabisulfite - 4.0 to 5.0 - acid

    Sodium Sulfite - 8.8 to 10.0 - somewhat alkaline.
    -- Ole Tjugen, Luddite Elitist
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  8. #28

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    "Very often, photographers who are accustomed to an acid fixer odor need to get used to the Alkaline pH fixer smell. The Alkaline pH fixer is more gentle than the acid."

    This was in the email newsletter sent out by Fine Art Photo Supply.

  9. #29
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    TF-4 has a mild ammonia smell--milder than, say, household ammonia. It&#39;s not odorless, but I&#39;m prone to respiratory problems, and I find it less uncomfortable to work with.
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  10. #30

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    A good non-acidic fixer is Agfa FX-Universal, primarily sold for colour processing, but ideal for B+W film and paper unless you need hardener. Diluted 1+5 it has pH=7.5 approx, so it's effectively neutral. It smells very slightly of ammonia. Much nicer in the darkroom. Also, it's relatively cheap.

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