Vit C dev sudden death

Discussion in 'Darkroom Developing and Printing' started by Jorge Omar, Sep 8, 2003.

  1. Jorge Omar

    Jorge Omar Guest

    I've been reading about vit C (ascorbic acid, ascorbate) devs
    andthat's what I know up to now:

    - It's a very nice combo with phenidone (or metol)
    - It suffers (or may suffer) sudden death.

    The main reason for sudden death seems to be iron contamination, and
    this poses a question:

    Shouldn't metal (inox tanks, spoons) be avioded with it?

    Thanks,

    Jorge
     
    Jorge Omar, Sep 8, 2003
    #1
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  2. Jorge Omar

    John Guest

    All metals should. Copper and iron in particular.

    Regards

    John S. Douglas, Photographer
    http://www.darkroompro.com
     
    John, Sep 9, 2003
    #2
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  3. It depends on the sort of iron. Some iron is bound to
    other molecules and isn't active. Most of the iron found in
    water supplies is this way.
    In any case, attributing iron in the water for the rapid
    loss of activity of ascorbic acid developers is mostly guess
    work. Thre are other possibilities.
    Iron containers should be avoided anyway because photo
    chemicals will oxidize them. Stainless steel of the right
    composition is OK for most chemicals but is slowly attacked
    by rapid fixer over time.
     
    Richard Knoppow, Sep 9, 2003
    #3
  4. Jorge Omar

    friend Guest

    ascorbic acid is oxidised easily by oxygen. Iron acts as a catalyst,
    making it faster. It is very well known for all chemists.
     
    friend, Sep 10, 2003
    #4
  5. Jorge Omar

    friend Guest

    photo grade chemicals are tested for certain impurities only, it is
    the lowest acceptable level. If you get analytical grade and most of
    lab grade chemicals, you should be fine.
    Plastic containers are OK, distilled water helps particularly is
    places with hard/very hard water. Heavy metals are not a problem in
    cities, but may be in rural areas (ground water).
     
    friend, Sep 10, 2003
    #5
  6. In the literature are strong indications that several chemicals _don't_ work
    as intended if used in analytical grade. These chemicals _need_ the
    impurities to work.

    So, if any chemical is offered as "photo grade" it is wise to use this
    grade. Your comment about distilled water is correct, usually you can
    omit Calgon, EDTA etc. from the recipes...

    Martin
     
    Martin Jangowski, Sep 10, 2003
    #6
  7. Jorge Omar

    friend Guest

    give me examples! I'm in this business for over 40 years and it's
    quite unusual statement.
    Facts??????
     
    friend, Sep 10, 2003
    #7
  8. Jorge Omar

    Nick Zentena Guest


    Which chemicals? Long term is there any reason to believe that those
    impurities will remain? I'm guesssing the majority of these chemicals are
    mostly made for other uses and if those impurities aren't need they could
    disappear any day.

    Nick
     
    Nick Zentena, Sep 10, 2003
    #8
  9. Jorge Omar

    friend Guest

    it does protect, but not as well as for example hydroquinone. There is
    an excess of sulfite comparing to ascorbate. There is bigger chance of
    sulfite ion react with oxygen. The redox potential varies depending
    on pH, and I do not have numbers handy. The higher pH, the faster
    oxidation of ascorbate, but most of developers based on ascorbates
    have relatively low pH. Sulfites do not react with oxidation products
    of ascorbic acid (unlike oxidised hydroquinone), so there is no
    reverse reaction bringing back vit.c. Once oxidised, it's lost for all
    practical purposes. Hydroquinone can be "regenerated"by sulfite.
    No, sulfites are not useless, rather less efficient.
     
    friend, Sep 11, 2003
    #9
  10. Jorge Omar

    Jorge Omar Guest

    Thanks, friend

    your posts still do not show up on Google...

    Jorge


    it does protect, but not as well as for example hydroquinone. There is
    an excess of sulfite comparing to ascorbate. There is bigger chance of
    sulfite ion react with oxygen. The redox potential varies depending
    on pH, and I do not have numbers handy. The higher pH, the faster
    oxidation of ascorbate, but most of developers based on ascorbates
    have relatively low pH. Sulfites do not react with oxidation products
    of ascorbic acid (unlike oxidised hydroquinone), so there is no
    reverse reaction bringing back vit.c. Once oxidised, it's lost for all
    practical purposes. Hydroquinone can be "regenerated"by sulfite.
    No, sulfites are not useless, rather less efficient.
     
    Jorge Omar, Sep 11, 2003
    #10
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