KRST: Hypo included - why?

Discussion in 'B&W: Film, Paper, Chemistry' started by Bob F., Apr 3, 2005.

  1. Bob F.

    Bob F. Member

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    I've had a look around and can't find out why selenium toner has hypo added.

    I mean, you fix the print, wash it, hypo clear it (optional), and then dump it in yet more hypo with the selenium toner... Seems odd, so there must be a logical reason for the hypo in selenium toner, but what? Anyone know? Do you really need it?

    Cheers, Bob.
     
  2. Bruce Osgood

    Bruce Osgood Membership Council

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    I have no idea why people do this but many do. I think it is counter productive in that hypo after selenium toning acts as a 'stop bath' and halts the toning effect. Hypo IN selenium toner seems to me would act as an inhibiter.
     
  3. MurrayMinchin

    MurrayMinchin Membership Council

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    Using an incredibly accurate scientific instrument - my nose - Kodak Rapid Selenium Toner (KRST) seems to be about 80% Ammonium Thiosulfate. I use 60% Ammonium Thiosulfate to mix up my own TF-3 alkaline rapid fixer. The KRST stock solution snaps my head back it smells so vile as compared to the 60% solution.

    Ansel said in The Print that selenium toner requires an alkaline environment to work...maybe its just a matter of Kodak finding the cheapest way to produce the stuff to maximize profits.

    Murray
     
  4. photobackpacker

    photobackpacker Advertiser

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    This is the first I have heard of this. I thought everyone mixed it with hypo clearing agent - I know, I do. Where are you reading about mixing it with fixer?
     
  5. Ole

    Ole Moderator Staff Member

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    Several misunderstandings here, I think!

    HYPO and Hypo-clear are two very different things. The first is an obsolete name for thiosulfate, the second is a commercial product used for removing thiosulfate.

    Kodak Rapid Selenium Toner - KRST - contains ammonium thiosulfate, and quite a lot of it too! I don't know why, but ammonium thiosulfate is a strong enough silver solvent that I can imagine it will speed up the toning process considerably.

    The recommendation to mix KRST with Hypo-clear has been abandoned, but is still printed on the labels AFAIK. I mix mine with water only.

    Stop calling any fixer "hypo", and we would all be a lot less confused.
     
  6. MurrayMinchin

    MurrayMinchin Membership Council

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    Actually, the KRST stock solution *itself* is about 80% Ammonium Thiosulfate...I think...sure smells that way to me. If correct, this means that all those people so set against rapid fixers have been using it all along if they selenium tone with KRST! Ironic isn't it?

    Murray
     
  7. Snapper

    Snapper Member

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    So, should we be giving prints that have already been washed, hypo-cleared, then washed again before going into KRST yet another wash-clear-wash treatment? I've just washed in the past, thinking tha a clear would be a waste of time. In that case, is there any point in washing/clearing prints before toning? I've noticed a purple/brown staining on prints that had not been thoroughly washed, and assumed that this was staining of left over fixer in the print.
     
  8. titrisol

    titrisol Member

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    I think Thiosulfate (ammonium) needs to be added to Selenium to achieve a Rapid toning.

    Tim Rudman has a very good explanation of this fact
     
  9. Donald Miller

    Donald Miller Member

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    This has been discussed ad nauseum in the past. The accepted procedure is two bath fixing with hypo (sorry Ole...old habits die hard and I am not about to change). The first hypo (Sodium Thiosulfate) bath includes Sodium Sulfite and the second does not. This is immediately followed (without washing) by toning in KRST. This is then followed with hypo clearing agent (it was called hypo clearing agent for a reason.) and then the print is washed for the recommended period of time to achieve archival permanence.

    The second hypo bath (without Sodium Sulfite) is saved for the next printing session and becomes the first fixing bath by the addition of Sodium Sulfite and a new hypo bath (Sodium Thiosulfate) is prepared for the second bath.

    If you will follow this procedure, I will imagine the staining you note will be eliminated.
     
  10. Bob F.

    Bob F. Member

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    Yup - thanks for clearing that up Ole - I did mean the Am. thiosulphate that is already in KRST (and others as far as I can tell). Sorry about the "hypo" - I was being lazy....

    Snapper: according to Tim Rudman (who I am inclined to believe on all such matters!) you are correct about the need to wash. According to his toning book, the two causes of staining are inadequate fixing and carry over of an acidic fix in the emulsion/paper to the toning bath - hence the need to wash. I could not find anything in his book that explained why the am. thiosulphate was included tho'.

    Ah... and as washaid/hypo-clear is, I think, alkaline, that would help reduce acidic carry over too which explains why it is sometimes recommended prior to the selenium toner (depending on whose book you read) and am. thiosulphate is also alkaline as Murray points out - so, no acid in the toner please...

    Cheers, Bob.
     
  11. Bob F.

    Bob F. Member

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    That makes sense: the second fixer bath is alkaline (prevents acid carry over) and ensures full fixing (unless you get really sloppy) - both of which cause staining. I have resisted the use of two fixer baths before now - I think that explanation from Donald has switched me over to using them as rather than being too much hassle, it will actually save time when using selenium...
     
  12. photobackpacker

    photobackpacker Advertiser

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    I am no chemist and can't tell you what each and every ingredient accomplishes in fixer. For that reason, I wouldn't disagree with what Don has posted.

    It does, however, differ from what I have learned in reading AA's book and in attending several of John Sexton's seminars. John follows Ansel's working methods in fixing and toning.

    He uses the Kodak F6 formula for fixer - reducing the amount of alum by 1/2. (Alum is an agent that hardens the emulsion.) The reduced alum aids toning.

    The second fixing bath is sodium thiosulfate dissolved in the concentration of 1/2 pound per gallon of water plus 1/4 pound of sodium sulfite per gallon. This differs from the F6 formula in that it contains no alum, no acetic acid and no kodalk (sodium metaborate).

    I use their process and have never had a problem with staining.
     
  13. Ole

    Ole Moderator Staff Member

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    Hmmm...

    The first fixer would do most of the fixing, and a bit of hardening.

    Then the second fixer is a very weak alkaline fixer, which leaches out the remaining silver salts, softens the emulsion, and neutralises the alum.

    So why use hardener at all, or indeed acid fix?
     
  14. hortense

    hortense Member

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    For many years I have made working solution of Se Toner by adding 1/4-teaspoon (heaping) Kodalk to 64-oz. of Selenium solution of whatever ratio I happened to choose (in other words, with water; no hypo-clear).
     
  15. Neanderman

    Neanderman Member

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    Per the MSDS, 27% by weight.
    The presence of thiosulfate does appreciably speed up the toning process (hence the Rapid in the name). I haven't found the definitive answer yet, but as mentioned above, thiosulfate is a silver solvent and will, in high enough concentration and/or after enough time, dissolve part of the silver in the image. This solvent action may, by increasing the number of silver ions present in the solution, speed up the formation of the silver selenide that provides the image color.
     
  16. dancqu

    dancqu Member

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    I've read that page on Adams' process routine. I tried to find that
    page a few months ago but think it has been deleted.

    After stop and first fix he used a holding bath. I can imagine that
    prints were held for hours prior to seeing the second fix. Sixty years
    ago, papers I believe, were not so prehardened as today. Like it
    or not, most if not all today's papers have incorporated
    hardeners. That is my understanding. Dan