Sodium Sulfite with Viradon?

Discussion in 'B&W: Film, Paper, Chemistry' started by photomc, Sep 9, 2004.

  1. photomc

    photomc Member

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    I know there are a few chemical types on this site..was wondering if anyone could help explain something for me. I was toning this weekend and decided to 'wash' the prints in some Sodium Sulfite after toning in Viradon. At the beginning of the session the Viradon was rather milky, as it usually is, let the first print set until I felt it was ready, then moved it over to the Sodium Sulfite tray, which cleared up the film that seems to be on the print after toning with Viradon, then decided to place the print back for a few more minutes.

    What happened were twoseparatee things - first the print seem to tone a little 'cleaner' and second, the toner cleared up...no milky look to it at all.

    Any ideas what the reaction was with the Na Sulfite and Viradon? It did appear to 'kill' the toning action after about 5 or 6 prints, but the tones were much more like I prefer - more chocolate than sepia.
     
  2. ann

    ann Subscriber

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    it will be interesting to hear (see) what the chemical experts have to say about this. Might have to give it a try. we use the sodium to stop the toning, then wash and then it need be start with the toner again.
     
  3. titrisol

    titrisol Member

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    I think Sulfite will stop the sulfiding of silver.
    Have to double check on Rudman's book and edit this item tomorrow
     
  4. photomc

    photomc Member

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    Ann, that was where I was going when I decided to put the print back into the toner after the Na bath, then realized what I had done. Ok, it is one of those things we do sometimes without thinking..anyway, since I treat most prints like a work print, I decided to continue and see what happened.
     
  5. Ole

    Ole Moderator Staff Member Moderator

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    I hope this will be legible without subscripts...

    Sulfur chemistry is an interesting field, which we use far more than we realise.

    Viradon is a solution of sodium polysulfide, Na2S(n) (the 2 and the (n) should be subscript - n simply means "any number from 1 and up")

    Sodium sulfite is Na2SO3 - again numbers in subscript. Just assume that from now on?

    Sodium sulfate is Na2SO4.

    Sodium thiosulfate is Na2S2O3.

    Sodium sulfide is Na2S.

    Polysulfides tend to decompose to sulfur and sulfide, as in Na2S(n) -> Na2S + S(n-1).

    The sulfur is the milky layer on the print, as well as the milkiness of the toner.

    Sodium sulfite reacts with sulfur to form thiosulfate, Na2SO3 + S -> Na2S2O3.

    It also reacts with oxygen to form sulfate, 2 Na2SO3 + O2 -> 2 Na2SO4.

    Thiosulfate can react with oxygen too, to form sulfate and sulfur. That's why alum/hypo toners work: 2 Na2S3O3 + O2 -> 2 Na2SO4 + 2 S.


    So what happened was that the sulfite carried over to the toner "absorbed" the free sulfur in the solution, turning into thiosulfate in the process. After too much sulfite has been added, there is no sulfide left to react with the silver, and the toner stops working!
     
  6. skahde

    skahde Member

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    (I'll use X_n for subscript and X^n for superscript like in TeX)

    This is *very* interesting! So we have an equlibrium between S_n (eg. S_1 to S_8) and Na_2S_(n) in the solution, the white deposit probably being the stable (and rather inactive) S_8.

    So if you lower the concentration of the polysulfide you will end up with less sulfur in the solution and S_8 is less likely to form. Does it sound reasonable that there is more reactive S_(n<8) in the solution at lower polysulfide-concentration and that this may be the reason for polysulifde-toners to speed up at higher dilutions?

    best

    Stefan
     
  7. Ole

    Ole Moderator Staff Member Moderator

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    Ah! I haven't written T_E\ X in many years!

    Trying to guess hat happens in such a solution is something I would leave to my University techer - professor Foss. He was nominated to the Nobel price for his work on sulfur chemistry!

    The S_n^2- ion is very soluble, unlike S_8 (which, to the uninitiated, means solid sulfur). The "n" is not limited to 1-8, there are chains as long as 14 (although they are a lot less stable than shorter chains)!

    Since a polysulfide chain can "drop" a sulfur atom without changing oxidation state, the reaction with silver is 2Ag + S_n^2- -> Ag_2 S + S_(n-1)^2-.

    Then since the silver is a solid, and the sulfur reacts "dirctly" with the metallic silver, the only influence of higher concentration would be to increase the amount of sulfur available for the reaction - so it should speed up with higher concentration.

    Since this doesn't happen, there must be some other reaction involved. My initial idea is that the lower concentration gives a proportionally higher concentration of thiosulfate (which will form in any aqueous sulfide solution). As we know the thiosulfate is a strong complexing agent for silver - that's why it's so good for fixing. So a relatively higher concentration of thiosulfate could "mobilise" the silver, causing it to react more easily with hte sulfide?
    A similar effect is the "development" of van Dyke prints in the fixer - the dissolving silver reacts with the Fe^2+ to form more solid silver. The darkening in the fixer is abrupt and very obvious; a case of fixer working as developer.
     
  8. ann

    ann Subscriber

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    my eyes have just rolled back into what is left of my brain :rolleyes: How about some :"cliff notes" for the chemical challenged:cool:
     
  9. Ole

    Ole Moderator Staff Member Moderator

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    Ehrrmmmm... I realise that that post was a lot easier to write than to read :wink:

    What happens is this: The sulfite dissolves the sulfur film on the print, turning into thiosulfate in the process.

    When sulfite gets into the toner, it again turns into thiosulfate and dissolves the sulfur ("milky").

    So the print tones a bit differently, since there's now fixer in the Viradon as well! Then after a while it stops working, because all the sulfide is used up or turned to thiosulfate. Prints don't tone too well in fixer :smile:

    Sulfite is a "magical" stuff - it absobs sulfur (turning to thiosulfate) and oxygen (turning to sulfate) both. Sulfate has very little use in photography, but thiosulfate is useful for dissolving silver halides ("fixing"). It also dissolves silver a little bit (or at least makes it easier for it to dissolve), so it helps to speed up some reactions - like sulfide toning and the iron/silver reaction in van Dyke prints.

    Still confused? You're not alone!
     
  10. photomc

    photomc Member

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    Ole and Stefan..Thank You, this is great. From the little chemistry I have had in college and working knowledge from a clinical lab I have a basic understanding now. Would also explain why the sulfer smell all but disappeared. Have to admit it was all a mistake, but I still like the results..will post one of the prints later today.

    Thanks everyone...Ann, wonder if there is a "Polysulfide Toning for Dummy's" - know I could use it right about now. :tongue:
     
  11. ann

    ann Subscriber

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    thanks , this i do understand,

    all those numbers remind me of how new students feel when we start throwing around fstops/sutter speeds:confused: