Kodalk from borax plus sodium hydroxide ...

Discussion in 'Darkroom Developing and Printing' started by lloyd, Oct 1, 2003.

  1. lloyd

    lloyd Guest

    oct103 from Lloyd Erlick,

    Recently the following formula for producing sodium metaborate
    (Kodalk) appeared in this ng. I don't understand how a hundred grams
    of sodium metaborate comes from about fifty five grams of reagents.
    Does the water in which all this takes place enter and make up the
    weight? Perhaps someone could correct the numbers ...

    100g sodium metaborate (Kodalk) == 45.45g borax + 9.53g NaOH

    lloyd, Oct 1, 2003
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  2. Think liquid solution;

    When I first got into making my own Metaborate I had email conversations
    with Maxim Muir who gave me some help. According to my proceedure
    Metaborate is mixed at a ratio of 1) part Sodium Hydroxide + 5) Parts Borax.
    Maxim went on to indicate that Kodalk is closer to an Octo-Hydrated version that
    appears the darkroom Cookbook, However the 1to5 version works fine for me.

    I use 25 grams of Sodium Hydroxide +
    125 grams Borax
    + 800 ml of water and stir
    + additional water to make a liter.
    Gregory W. Blank, Oct 1, 2003
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  3. lloyd

    Jorge Omar Guest

    I believe this formula to be fairly right, but see:


    I'm having trouble with this mix since NaOH absorbs a lot of water and
    CO2 from the air and results are not repetitive, so pH changes from one
    lot to the next.
    I'm considering using a NaOH liquid solution to see if I get more
    constant results.


    wrote in 4ax.com:
    Jorge Omar, Oct 1, 2003
  4. I use the CRC Handbook definition of sodium metaborate which includes 4
    molecules of water. Borax has 10. NaOH has none. The water it absorbs
    from air is not part of the crystal. If you leave a bit of NaOH out,
    after while you will have a puddle of NaOH in solution.

    When you calculate the solution percent, don't forget that when you
    dissolve the metaborate, a large part of its weight is water of
    Patrick Gainer, Oct 1, 2003
  5. Dissolve your NaOH in distilled water and keep adding the lye until no more
    will dissolve and the solution is saturated with a few crystals in the
    bottom of the jug... At that point you have saturated solution... A
    measured amount of the saturated solution should always result in the same
    pH in your chemistry...
    Dennis O'Connor, Oct 1, 2003
  6. lloyd

    Jorge Omar Guest

    Thanks, Dennis

    Do you know the saturation percentage for NaOH?

    Jorge Omar, Oct 1, 2003
  7. Oh gaaawwd.... It's been nearly 50 years since inorganic chemistry, and I
    don't have a Chemistry Handbook here at the office to look up the
    solubility... But, from the hazy memory of a voice murmuring across a
    sleepy classroom over a half century ago that a saturated solution of lye
    requires equal weights of lye and water...

    So, a saturated NaOH solution can be prepared by mixing equal weights of
    NaOH pellets and distilled water. The saturated lye should stand for several
    days to allow the carbonates to precipitate. Only the clear upper solution
    should be decanted leaving the precipitates/carbonates in the bottom... If
    the pellets are fairly wet, meaning they contain considerable water already,
    you may want to reduce the weight of the distilled H2O by 10% <or some such>
    so that you are sure of it being a saturated solution... If there is a
    powdering of lye still undissolved in the bottom after 2 or 3 days, it is
    If I misremember a saturated solution of NaOH as being equal in weight to
    the water it is dissolved in, someone may correct me..
    Cheers ... Denny
    Dennis O'Connor, Oct 1, 2003
  8. lloyd

    Jorge Omar Guest

    Thanks again, Dennis

    Not very easy, but doable...

    Jorge Omar, Oct 1, 2003
  9. There was a rather extensive discussion of the hydration
    of Kodalk in the Pure-Silver list recently. While Kodak has
    always refered to Kodalk as the octahydrate it seems likely
    that it is actually the tetrahydrate. In any case,
    tetrahydrate can be used for Kodalk with equal results in
    all the old formulas.
    Richard Knoppow, Oct 1, 2003
  10. I once bought 25 lbs of Kodalk. I'm pretty sure it said it contained the
    tetrahydrate, but that was about 30 years ago. Like all the other
    things, the label only said "contains" and not "consists of". I don't
    know for sure what the equilibrium form might be for the crystals, but I
    suspect the tetrahydrate. That and the anhydrous are the only ones
    listed in the CRC Handbook unless you count the perborate, which
    contains one peroxide and 3 waters.

    I always read your posts first if there's one in the thread. I couldn't
    get through your spam filter to mail you directly. How come you got
    through mine?

    Pat Gainer
    Patrick Gainer, Oct 2, 2003
  11. lloyd

    friend Guest

    pretty close. solubility of sodium hydroxide monohydrate is 109.2 g in
    100 g of water at 20°C, 126 g at 40°C, 178 g at 60°C, and sodium
    hydroxide (anhydrous)313.7 g at 80°C.
    at 20°C total content of saturated NaOH is 52.2%.
    friend, Oct 2, 2003
  12. lloyd

    friend Guest

    just fuse one part of borax with one part of sodium carbonate.
    commercial metaborate has variable hydration.
    when you mix hydroxide with borax it is safer to have an excess of
    borax, rather than excess of hydroxide.
    one mole of borax reacts with two moles of sodium hydroxide giving
    four moles of metaborate.
    friend, Oct 2, 2003
  13. lloyd

    Jorge Omar Guest

    And at what temperature will this fusion take happen?


    Jorge Omar, Oct 2, 2003
  14. lloyd

    Dan Quinn Guest

    RE: wrote
    I'm quite sure that formula is Dr. M. J. Gudzinowicz creation. I've
    wondered about that equality for some time.
    The borates derive form the corresponding acids of boron. There
    are ortho, meta, and tetra boric acids and borates. The acids are
    H3BO3 (ortho), which on warming yields HBO2 (meta), and that on
    warming yields H2B4O7 (tetra). The borates become progresively
    In water at usuall temperatures, they all revert to the ortho
    form. That is both the tetra and meta convert to the ortho form.
    So what goes? It must be kept in mind that the borate form
    itself changes. Hydration in this case goes beyond, mono,
    penta, etc, H2O hanging on at the end of some borate.
    Solubility may be what goes. At room tempeature the meta is at
    least five times more soluble.
    The doctor has said that 100gr NaBO2 = 45.45gr Na2B4O7 + 9.53gr
    NaOH. I'll convert all the borates on each side of the equation
    to ortho and then we will know. Dan
    Dan Quinn, Oct 3, 2003
  15. lloyd

    friend Guest

    around 700-800°C, easy with Bunsen burner or an oven.
    Borax melts around 740.
    friend, Oct 3, 2003
  16. lloyd

    Jorge Omar Guest

    I've seens lots of postings on how to mix metaborate, tried them and I
    would say that without first making a saturated NaOH solution it is
    nearly impossible to make a correct solution.

    A question for the chemists over there:

    If one adds excess NaOH, metaborate crystals will precipitate (both as
    powder like and real crystaline structures).

    Would decanting the liquid and drying the crystals be Ok or, as I think,
    the crystals will have a lot of NaOH contamination (at least in the
    surface) in it?



    (Dan Quinn) wrote in
    Jorge Omar, Oct 3, 2003
  17. lloyd

    Jorge Omar Guest

    I'm afraid I couldn't do it in my kitchen...

    Jorge Omar, Oct 3, 2003
  18. The formula I gave you I know will work however if getting all
    the chemistry into solution is your goal, try mixing half strength
    that is: same amount of chemistry + plus twice the water then use twice
    as much solution in the end....works like a charm.
    Gregory W. Blank, Oct 3, 2003
  19. Provided that the ratios are correct if your mixing the solution in
    water between 100F and 120F it should go into solution, but does
    require some stirring.
    Gregory W. Blank, Oct 3, 2003
  20. lloyd

    Jorge Omar Guest


    I know the formula works - I've mixed it a few times.
    The problem I'm having is that, according to the Rio Tinto site, a 1%
    metaborate solution will have a pH of 11 and 11.44 for a 5%.
    I always measure less than that (the NaOH absorbs water and its weight
    increases); then I have to add (slowly) more NaOH until the pH is right
    (tritation like).
    If one overdo the NaOH, it will cystalize as soon as temperature goes
    down, and pH will rise to over 12.
    Add to that my not very stable pH meter (Hanna Checker) and it becomes a

    I just whish I could find a source for small quantities over here

    Jorge Omar, Oct 3, 2003
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