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  1. #1
    JDP
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    Mixing a Borax solution - precipitation observed

    Hello All,

    I have a question regarding a Borax solution I recently mixed. This was for part 2 of a split development for B&W (the first part was Microdol-X). The second part was the Borax solution which was simply 20 grams of Borax per litre of tap water. The tap water was first filtered with a domestic water filter, then boiled (and allowed to cool) to reduce hardness, then used for mixing (this is my normal proceedure).

    The Borax dissolves easilly, but each time I have done this, a few hours afterwards, a white precipitate appears in suspension, which looks like snow, or teased-out cotton wool. I tried storing the solution in both HDPE and glass bottles, with the same result. I have not managed to get the precipitation to re-disolve. I have no idea what it is or why it has formed (other impurities in the water/Borax powder?)

    If I use the solution before the precipitation forms then it works fine and the negatives are good. I have not tried developing a film with a solution showing the precipitation!

    Any comments on this would be appreciated.

  2. #2

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    Boiling water will not reduce "hardness." The problem is dissolved minerals, and if anything, boiling the water will increase the concentration of dissolved minerals. Try using distilled water next time. If you can't get distilled water, filter the precipitate and run a test roll. You likely will want to use distilled water for your final rinse before drying the film if your water is very hard.

    Peter Gomena

  3. #3
    desertrat's Avatar
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    I also get a precipitate when I mix a Borax solution, and some of it gets through the coffee filters I use for filtering. In this case, time, gravity, and sedimentation are our friends. Wait until the solids settle on the bottom of the container in a thin layer. This could take anywhere from overnight to several days. Then carefully draw liquid off the clear upper layer for use.
    Happiness is a load of bulk chemicals, a handful of recipes, a brick of film and a box of paper. - desertrat

  4. #4

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    +1 on the distilled water. I use it to mix ALL chemicals, I wash in filtered tapwater, and final rinse with distilled water with a drop or so of Photo-phlo.

  5. #5

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    Another vote for distilled. You should also check your borax. Several years ago, one of the raw chem photo suppliers had a batch that wouldn't dissolve, but I've not seen a difference between the 40 Mule Team brand and that sold by chem suppliers.

  6. #6
    Mike Wilde's Avatar
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    I have found a simiar challenge making up the B alkali with Kodalk, sodium metaborate for use in PMK Pyro. It will not fully dissolve unless your use distilled.
    my real name, imagine that.

  7. #7

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    Boiling of tapwater only removes the "temporary hardness" ,mostly bicarbonates which decompose to the insoluble carbonates.It leaves in solution the "permanent hardness" including calcium sulfate.When borax is added this produces calcium borate which is insoluble and precipitates out.

  8. #8

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    I knew someone out there would have the actual chemical reason for this. I haven't studied chemistry in more than 35 years, so I wasn't going to guess.

    Peter Gomena

  9. #9
    JDP
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    Quote Originally Posted by Alan Johnson View Post
    Boiling of tapwater only removes the "temporary hardness" ,mostly bicarbonates which decompose to the insoluble carbonates.It leaves in solution the "permanent hardness" including calcium sulfate.When borax is added this produces calcium borate which is insoluble and precipitates out.
    Ah-Ha! Thanks for this. I was aware of the 'temporary hardness' but not the reacion of borax with calcium. My water is very hard so even with boiling/filtering there must be enough dissolved calcium still present.

    Only thing is distilled water round here costs one UK pound per litre! I thought of buying or building a device to make my own, but am uncertain how cost-effective that would be.

  10. #10
    JDP
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    Quote Originally Posted by desertrat View Post
    I also get a precipitate when I mix a Borax solution, and some of it gets through the coffee filters I use for filtering. In this case, time, gravity, and sedimentation are our friends. Wait until the solids settle on the bottom of the container in a thin layer. This could take anywhere from overnight to several days. Then carefully draw liquid off the clear upper layer for use.
    So it looks like the solution is still useable - thats good to know!

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