Kodak ST-1 Test for residual silver

Discussion in 'B&W: Film, Paper, Chemistry' started by Marco Buonocore, Mar 26, 2009.

  1. Marco Buonocore

    Marco Buonocore Member

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    Hello there,

    A couple of quick questions with regards to the ST-1 test process:

    Once the paper has been fixed, is the paper given a full wash and then tested, or does the test take place directly after fixing?

    If there is a wash inbetween fixing and testing, would a hypo clearing bath interfere with results?

    Thanks!
     
  2. ic-racer

    ic-racer Member

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    I just give a quick rinse, but someone may have a better answer.
     
  3. dancqu

    dancqu Member

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    The ST-1 test uses sodium sulfide as a test for silver. If silver
    is present a silver sulfide stain will be produced. Fixers work by
    forming soluble complexes with the other wise insoluble
    undeveloped silver halides in the emulsion. So the
    fixer carries silver.

    The test's sulfide will combine with that attached silver and
    give a false reading. Give the paper a thorough cleaning. Hypo
    clear after fixing only assists in the removal of the fixer. Dan
     
  4. Photo Engineer

    Photo Engineer Subscriber

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    Wash only, for the prescribed time and method for your paper and fixer. Then apply the test.

    PE
     
  5. Marco Buonocore

    Marco Buonocore Member

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    Thanks! Exactly the information I needed.
     
  6. dancqu

    dancqu Member

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    A correction.

    That within quotes is incorrect. The fixer's action is to form
    soluble silver compounds. The halide be it chlorine, bromine,
    or iodine, is not a part of the complexes formed twixt the
    fixer and silver.

    The thiosulfate ion is the primary agent in removing the
    silver and in the presence of iodine the only agent with
    the necessary affinity. The ammonium ion's affinity
    for silver is much less. So, with films containing
    extremely insoluble iodized silver rapid fixers
    become slow fixers. Dan
     
  7. BobNewYork

    BobNewYork Member

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    Dan:

    Am I wrong in thinking that today's film emulsions increasingly use silver iodide? If so, does that mean that sodium thiosulphate is a better fixer for modern emulsions?

    Bob H
     
  8. jim appleyard

    jim appleyard Member

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    IDK, but according to Anchell/Anchell & Troop, he/they speculate that sod. thio is inferior to ammon. thio with newer emulsions. I'll have to look up the exact quote/phrase.
     
  9. BobNewYork

    BobNewYork Member

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    Maybe I've got it wrong about increased use of iodide in modern emulsions - I just seem to recall reading it somewhere. I know that Bill Troop and Steve Anchell concluded that ammonium thio was better for modern emulsions, that's why I was surprised when Dan pointed out that ammonium doesn't fix well in the presence of iodides. I tend to overfix (8 minutes) anyway as ammonium doesn't reduce density like sodium in extended fixes. The only reason I do it though is because I limit my 1.5l of fixer to twenty films and use the three times clearing rule based upon the last batch. That way my fixing time is standard each time. My brain hurts a little less that way!!

    Bob H
     
  10. Photo Engineer

    Photo Engineer Subscriber

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    Modern emulsions use up to 10% iodide, but emulsions from about 75 years ago were typically maxed out at about 3%. Fixing with Ammonium Thiosulfate is always faster regardless of emulsion type, so in a difficult situation the Ammonium salt is the way to go. Since Iodide represents only a max of about 10% of the halide present, the effect is not huge, but can be seen, particularly in exhaustion of a fix used with high iodide films.

    PE
     
  11. BobNewYork

    BobNewYork Member

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    Thank you sir. Appreciate it.

    Bob
     
  12. dancqu

    dancqu Member

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    As for the amounts of silver iodide in today's emulsions over
    years ago, I think Ron has answered that question. I seem to
    recall some to-do over the Delta and T films when brought to
    market around 20 years ago. Particular note was taken of
    their iodide content. I'm quite sure there must be some
    update versions of older emulsions which do not have
    significantly increased iodide content. Certainly not
    the increase seen in the T grain films.

    Sodium has no affinity for silver so takes no part in the
    removing of silver. Ammonia in solution does have some
    affinity. I've read of it being used alone as a fixer in the
    case of chlorided only silver emulsions. The chloride of
    silver is the most soluble of the silver halides.

    At the other extreme is silver iodide. It and silver sulfide
    are two most insoluble salts of silver. The ammonium ion
    has nearly no effect upon the iodide while the thiosulphate
    ion with it's greater affinity for silver will, in some surplus,
    clear the silver from an emulsion.

    In all cases, chloride, bromide, or iodide, the ammonium
    ion acts as a fixer; the more so with the chloride and least
    so with the iodide. Temporary though is it's attachment to
    silver because the thiosulfate ion, with it's much greater
    affinity for silver, 'steals' the silver from the ammonium
    ion. Both the ammonium and thiosulphate ions are
    active in attaching silver where rapid fixers are
    used. So Ron, on a technicality, is correct.
    Rapid fixers are faster in all cases. Dan
     
  13. Photo Engineer

    Photo Engineer Subscriber

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    Well, to get a bit more specific and technical, Sodium takes no part in the fixing reaction other than being a balancing positively charged ion in the fixer. Ammonium ion takes part in the fixing reaction by being a silver complexing agent itself. So, both Ammonium and Thiosulfate ions take part in the fixing action and their action is superadditive. In addition, the Ammonium ion is a positively charged ion in the fixer, and it is about 2/3 the size of a Sodium ion and much much smaller than Thiosulfate.

    Therefore, wherever Ammonium ion replaces Sodium, the complex of Silver + Thiosulfate is smaller by a rather huge amount, and therefore diffuses out of the coating more rapidly.

    You therefore have several things on your side in Ammonium Thiosulfate fixes. The superadditivity, size and diffusivity effects all add up to increase fixing rate.

    Halide ions of any sort slow fix rate down, and therefore buildup of halide with use slows down fixation by helping to exhaust the fix. The fix is exhausted two ways, by buildup of halide ions and by use of Thiosulfate ions. But, in Ammonium Thiosulfate fixes, since both Ammonium ion and Thiosulfate ion are complexing agents, the fixer has an effective concentration of useful complexing agent of about 2x that of a comparable Sodium Thiosulfate fix. It can be even larger, depending on pH and the nature of the 5 or so complexes that can form between the various reactants.

    By analogy, larger ions slow down fixation and therefore you must NEVER mix a fix with Potassium Thiosulfate or Calcium Thiosulfate or Magnesium Thiosulfate, as these large positive ions will effectively poison a fix.

    There is fixing in a larger expanded version.

    PE
     
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  15. BobNewYork

    BobNewYork Member

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    WOW! I had to ask, didn't I:D

    Appreciate the insights guys. So it Ammonium all the way for me.

    BTW PE - someone on another thread who shall remain nameless, :tongue: is accusing you of suggesting that C-41 fixer, (buffered Ammonium Thio as far as I know) is not suitable for B&W work. Why would that be?

    Bob H
     
  16. Photo Engineer

    Photo Engineer Subscriber

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    Bob;

    The C-41 fixer is usable for color and B&W. Many B&W fixers are not suitable for color. It is a question of pH.

    Now, to go further, the C-41 RA fixer may not be suitable for some B&W films because of the chemical composition of the fixer and the hardness (or lack thereoof) of certain films.

    So, it may depend on fixer and film.

    PE
     
  17. RPC

    RPC Member

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    So, for B&W, should regular C-41 fixer be used at normal strength for both film and paper?

    RPC
     
  18. Photo Engineer

    Photo Engineer Subscriber

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    Well, what is the "normal" concentration of C-41 fixer for paper. There are no suggestions by Kodak. And, due to the different level of silver in B&W and color, what is the normal concentration for B&W film?

    You can use it, but you are on your own and you must use your own testing to determine that.

    PE
     
  19. RPC

    RPC Member

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    By normal, I meant working solution strength for C-41. For B&W, would you suggest starting testing at that strength for film and paper and just adjust times for 2x clearing? I was thinking that for paper it might be diluted some, perhaps half working solution strength.

    RPC
     
  20. Photo Engineer

    Photo Engineer Subscriber

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    IDK your paper, film or workflow. The only way to be sure is by testing with the retained hypo and retained silver tests. You would have to do that. Otherwise there are no suggestions anywhere for the correct values of color for use with B&W.

    PE
     
  21. BobNewYork

    BobNewYork Member

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    OK - starting to breathe a little easier!!

    I've done the tests with Tri-X, TMX and TMY, (the older version) and they were fine. Also done then with Polymax, Polymax-Art, Polycontrast, MGIV and MGWT - fine again. I use the C41 fixer replenisher diluted 1+4 for both film and paper - though I'm sure a higher dilution would be fine for paper.

    Thanks PE - feeling better!!

    Bob H
     
  22. RPC

    RPC Member

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    What were your times for TMX and MGIV?

    RPC
     
  23. BobNewYork

    BobNewYork Member

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    I use 10 min for all films and 2 min for paper. Paper fix I toss and the end of each session.

    For film I mix up 1.5 litres of working strength, (because that's my largest tank). I figure a recommended 25-30 films per litre and a half and do only twenty, (or throw it after the first batch that takes me over 20.) I tested clearing times after 20 films and it was 3 minutes. Based on the Anchell / Troop recommendation of 3X clearing I do them all at a 10 minute standard time. The reason I'm not so bothered about over-fixing is Troop / Anchell again who suggested that ammonium thio doesn't begin to bleach like sodium thio. Seems to work for me. I would probably test for each batch if I used sodium thio as over-fixing is as bad as under-fixing by all accounts.

    Bob H
     
  24. dancqu

    dancqu Member

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    I haven't the Darkroom Cook Book so do not know just what
    was written with regard to sodium thio and bleaching of the
    image. With 150 years of it's use the darkroom community
    should have well in mind it's short comings and how well
    it compares with A. Thio.

    Comments this NG usually refer to a very protracted fix
    being a cause for bleaching. Most commentary refers to
    A. Thio. Most use A. Thio.

    A. or S. Thio., the essential ingredient is thiosulfate
    which is by itself, if anything, a reducing agent.

    S. Thio. as a dry concentrate with Very long shelf life
    works well with my current low volume of darkroom
    work. I mix it fresh each session, film or paper.
    Good for a session with no additives. Also
    odorless. I believe Anchell's 'plain' fix
    is no more than S. Thio. Dan
     
  25. BobNewYork

    BobNewYork Member

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    You're absolutely right Dan. One shot, right time - sodium or ammonium doesn't matter,they both do a good job.

    I go through stages where I may process between 5 and 20 or more films a day so I just wanted to standardize my time without having to run clip tests for each tank load. This way I know that all my films are properly fixed and I felt more comfortable with amm. thio. Also means one fixer, one dilution for my film and paper. The fewer variables I have the less prone I am to screw up. And, trust me - I'm well prone to screwing up.:tongue:

    Bob H
     
  26. Photo Engineer

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    Acid fixes are more prone to bleach highlights in images than neutral or alkaline fixes. It is a very slow reaction requiring a half hour or more to see any reaction, so I would not worry too much about it.

    PE