Potassium Bromide

Discussion in 'B&W: Film, Paper, Chemistry' started by i.candide, May 12, 2012.

  1. i.candide

    i.candide Member

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    Hi, I'm going to ask a newbie question...eventually.

    Background: I want to start developing film in caffenol and just took delivery of a Photographer's Formulary bottle of potassium bromide. I expected powder or small crystals - but got large one inch crystals.

    Question: What is the easiest and quickest way to efficiently and effectively get the crystals to a powder or very small crystals? The recipe calls for 1 to 2 grams per litre.

    Can anyone advise using appliances found in a normal household?

    Thanks,
    i.candide
    Dangerous to oneself
     
  2. Peltigera

    Peltigera Member

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    Pestle and mortar. But be sure to clean it well - KBr is not that good for you.

    Failing that, a coffee grinder - but the crystals might be harder than the grinder is designed to cope with.
     
  3. georgegrosu

    georgegrosu Member

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    I have not seen large crystals of potassium bromide. I saw large crystals (~ 2 cm) of sodium thiosulphate.
    Do 50 ml ~ 20% solution in water and put a piece of not developed film.
    If the film becomes transparent is sodium thiosulfate.
    To test if is potassium bromide you should have a silver nitrate solution.
    George
     
  4. MrclSchprs

    MrclSchprs Subscriber

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    Have a look at Caffenol. There you will find at least three different recipes for a coffee based developer. One for slow and medium speed films, one for stand development and one for fast films. The first developer does not need KBr. Check it out, it contains valuable information.
     
  5. john_s

    john_s Subscriber

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    One way might be to dissolve the whole lot in water and use it as a stock. Mine is 100g/Litre. It's also handy if you want to add some to paper developer to get warmer tones.
     
  6. jochen

    jochen Member

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    Hello,
    put the large crystals in a clean and stable plastic bag, lay it on the floor and take a hammer.
     
  7. Marco Buonocore

    Marco Buonocore Member

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    Making a 10% solution is the way to go. I make 1l and go through it pretty quickly making bleach and developers.

    Potassium bromide dissolves well in hot (125 f) water.

    Trying to measure out 1 or 2g of the stuff from raw chemistry is a big pain.
     
  8. HTF III

    HTF III Member

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    Does a 10% solution of KBr go bad? That's a dumb question. Better put, how long before it spoils? Thx
     
  9. MrclSchprs

    MrclSchprs Subscriber

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    No, it does not go bad.
     
  10. Mainecoonmaniac

    Mainecoonmaniac Subscriber

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    Can't you just use large crystals? I have a 20 year old jar with large crystals and I weight it out then dissolve in hot water as needed.
     
  11. Doremus Scudder

    Doremus Scudder Member

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    I like to keep a potassium bromide solution around for a number of purposes. I would just weigh your large crystals, make the 10% solution and use it as you need. It will last forever. Then you can use it to mix developers of all kinds, as well as as a restrainer-additive for your print developer and as a component of a rehalogenating bleach together with a potassium ferricyanide solution.

    Best,

    Doremus


    www.DoremusScudder.com
     
  12. pdeeh

    pdeeh Member

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    So, just to clarify for people like me (gave up mathematics and chemistry age 14, find ratios difficult to grasp sometimes, has to calculate the dilution on a scrap of paper each time I make up some developer) ...

    10g/l = 1% solution
    100g/l = 10% solution
    200g/l = 20% solution ... and so on, up to the solubility limit of KBr in water I presume.

    SO, when I am making up a litre of developer that requires 1g of KBr per litre, I would substitute 100ml of a 10% solution for 100ml of the total volume of water required by the formula ?

    (I imagine a lot of sighing, eye rolling and shaking of heads from all the scientificky types at this point)
     
  13. madgardener

    madgardener Member

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    You aren't the only one who isn't mathematically inclined. While I would like to try some of the home brewed chemicals, I limit myself to the stuff that's pre-mixed/portioned, precisely so I don't have to calculate anything. Math and me do not get along, so don't worry about you being alone. :smile:
     
  14. GregW

    GregW Member

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    So..wait a minute. Still not getting it. :wink:
     
  15. Jim Taylor

    Jim Taylor Member

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    Yes - this is correct! :happy:
     
  16. pdeeh

    pdeeh Member

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    Hurrah!
     
  17. anikin

    anikin Subscriber

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    No quite 100ml. You see, 100ml of 10% solution contains exactly 10g of KBr. If you need 1g, you use 1/10th of it, or 10ml, not 100.

    Think of it in terms of bromide in the bottle. Say you dissolved 100g of KBr in some amount of water. If a formula calls for 50g of KBr, you use half of the solution, if a formula calls for 1g, you use 1/100ths of the solution, 5g - 5/100ths, etc.
     
  18. pdeeh

    pdeeh Member

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    thank you for the (completely obvious now you point it out) correction

    Really, it's a wonder sometimes that I've managed to develop any film or prints at all, or even make a cup of tea. Although I suppose making tea doesn't require the ability to divide by 10 correctly.

    jeez