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  1. #1

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    Sodium Thiosulphate and modern papers

    Is Sodium Thiosulphate fixer capable of fixing todays papers? I know it's slower but is it as efficient as Ammonium?

  2. #2
    Ian Grant's Avatar
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    Simple answer is yes it just need a longer time in the fixer.

    Ian

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    Wasn't one of the late Kodak papers (Polymax FB?) difficult to fix and was therefore recommended to use rapid fix only? I uderstand it's iodine that slows down the process of fixing very much and that Sodium might not work at all.

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    One of the last Kodak papers was indeed difficult to fix, but using longer times solved that problem. However, there is no obvious problem with any of the modern problems if you use enough time.

    Remember that the retained Silver solution will tell you if there is any Silver left. Also, with longer times, use better wash.

    PE

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    Thanks to both.

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    Out of curiosity I went and checked the msds of sodium thiosulphate and under the Section 10 - Stability and Reactivity there is a paragraph Incompatibilities with Other Materials saying it's not compatile (among other things) with silver salts and iodine.

    I'm missing a bigger picture here...

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    Ian Grant's Avatar
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    Quote Originally Posted by miha View Post
    Out of curiosity I went and checked the msds of sodium thiosulphate and under the Section 10 - Stability and Reactivity there is a paragraph Incompatibilities with Other Materials saying it's not compatile (among other things) with silver salts and iodine.

    I'm missing a bigger picture here...
    Yes it's not compatible with Silver salts and Iodine, it reacts with them to form complexes, which is exactly what we want in photography but we need to ensure that the silver/thiosulphate complexes are water soluble. Too high a level of silver and the complexes are less water soluble and too high a level of Iodide inhibts the process.

    Ian

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    Wonderful! Thanks Ian.

  9. #9
    AgX
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    A series of complexes is formed, only a later one will be watersoluable. That is why time is of importance.

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    Quote Originally Posted by AgX View Post
    A series of complexes is formed, only a later one will be watersoluable. That is why time is of importance.
    Yest, the fixing time should be as short as possible and there is also the need for a second fixing bath so that Ag(S2O3)- which is insoluble turns into Ag(S2O3)2- and Ag(S2O3)3- which are soluble.

    I also found an answer by Richard Knoppow that I would like to share here (it tells what Ian and PE said already):

    Ammonium thiosulfate fixers are less sensitive to soluble iodide
    from fast emulsions. Sodium thiosulfate fixing baths are slowed down
    by accumulated iodide but continue to fix the emulsion, they simply
    need more time.
    The use of a two bath fixing system eliminates to a great extent the
    problem of accumulated iodide since nearly all of it comes out in the
    first bath, leaving the second bath working at full speed.
    Two bath fixing has the same advantage for rapid fixers that it does
    for sodium fixers, namely the capacity for archival fixing is extended
    by four to ten times and the relatively fresh second bath assures
    complete solublization of the silver complexes.

    The rapid fixers made by adding ammonia salt to a sodium fixer are
    not quite the same as rapid fixers made with ammonium thiosulfate.
    They are not quite as rapid.

    As far as what types of films and paper have silver iodide in them,
    all reasonably fast films are made with silver iodide. That means even
    slow pictorial films like the late, lamented Agfa Agfapan-25. Faster
    films, like Tri-X have an abundance of iodide, and the newer tabular
    grain films also have a lot. Kodak recommends longer fixing times for
    Tri-X as they do for T-Max films. Both can be fixed in sodium
    thiosulfate fixers, provided enough time is alloted for complete
    fixing.
    The old rule of thumb is to allow double the clearing time for
    complete fixing. You will find the clearing time for T-Max nearly
    twice that for a film like Plus-X or Verichrome Pan. Some recommend
    fixing T-Max for three times the clearing time. I think this is
    unnecessary when a two bath fixer is used.

    Its possible that some paper has silver iodide in it but I don't
    know specifically which ones. Traditionally, paper is made with silver
    chloride, silver bromide, or a mixture of the two. For the most part
    the extra sensitivity given by siler iodide is not necessary for
    paper. Most paper emulsions will fix out in a minute in fresh sodium
    thiosulfate fixer when the print is fixed alone. Much longer fixing
    times have traditionally been recommended to compensate for the use of
    partially exhausted fixer and the fixing of many prints together,
    preventing adequate access of fresh fixer solution to the surface.
    Fresh film strength rapid fixer will fix out most paper emulsions in
    30 seconds. This is the basis of the Ilford archival processing
    method. Its purpose is to fix out the paper quickly enough to prevent
    substantial adsorption of the fixer to the paper fibers.

    Clearing time for film can be observed directly. A clip of the
    unprocessed film is soaked in water for a few minutes and placed in
    the fixer. Agitate it gently and measure the time until it becomes
    transparent. Fixing time is generally twice the clearing time. The
    reason for soaking the film first is that wet film fixes at a slightly
    different rate than dry film. When dry the emulsion must swell first
    for the solution to fully penetrate it. In practice, the film is
    wetted and swollen when introduced into the fixer.
    Please not that partially exhaused fixer can still clear the film,
    but, if there are not enough thiosulfate ions left, it can not
    complete the somewhat complex reaction that results in the reaction
    products being soluble in water so they will wash out.
    The two bath system insures these reactions will be completed and
    the reaction products will wash out.
    Any silver complex left in the emulsion will eventually decompose
    and attack the image. Once the film has dried these reaction products
    begin to change, so that even subsequent fixing in fresh fixer may not
    make incompletely fixed film or paper permanent.

    This is much more than I intended to write. I hope it is helpful
    rather than confusing.
    To summarize:
    Conventional sodium thiosulfate fixer is suitable for high iodide
    films, providing a two bath fixing system is used.
    All pictorial films have some silver iodide, but fast films have
    more.
    Some paper may have silver iodide but it is not traditionally used in
    paper emulsions.
    A kind of rapid fixer can be made without ammonium thiosulfate by
    adding ammonium salts to conventional fixer.
    Even rapid fixer is not a gurantee of complete, archival, fixing. A
    two bath system with either type of fixer is a large help.
    I will add finally that the use of a fixing bath test solution is
    helpful in keeping track of fixing bath condition. The formula and
    instructions for Kodak FT-1 is given in the _Kodak Black-and -White
    Darkroom Dataguide_. I prefer this to the prepared Edwal Hypo Check
    because the Kodak formula is of known strength and specific dilution
    is given for testing various types of baths.
    The same book has the formula for the residual silver test ST-1,
    whichis a 2% solution of Sodium Sulfide. A 1:9 dilution of Kodak Rapid
    Selenium Toner can also be used to test for residual halide. A few
    drops are applied to the wet emulsion and allowed to work for about
    two minutes. The emulsion is then blotted and examined for any stain.
    Either solution will stain silver halide. There should be NO stain if
    the film or paper is completely fixed.

    Enough !
    ---
    Richard Knoppow
    Los Angeles, Ca.

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