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  1. #11

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    Quote Originally Posted by kept View Post
    Thank you all very much for the answers!
    It's funny though I've found an old glass vessel almost full of potassium dichromate (according to the formula written on it) in an old photo lab. It's a bit strange it is a white powder not red, as I saw it in Wikipedia. Is it still good to use? Does potassium dichromate have an expiry date?
    As a chemist I can't think of any chromium salt that is white. So I would say that it's definitely not potassium dichromate. The element chromium gets its name from the color of its compounds.

    There is an easy test to identify potassium dichromate. Dissolve a small amount in water and a few drops of 3% hydrogen peroxide. A dark blue color is produced which soon fades with the evolution of oxygen bubbles.
    Last edited by Gerald C Koch; 08-14-2012 at 11:11 PM. Click to view previous post history.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

    ~Antoine de Saint-Exupery

  2. #12

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    Hi, this is a question for discussion purposes rather than me making a knowledgeable statement:
    If potassium dichromate is used to tan the gelatin, making it hard and stable, would an alternative tanning agent act as a suitable replacement?
    I originally trained as a leather technician, many many years ago, but remember the following: chrome VI salts are most commonly used mineral tannages, with pyrogallol and catechol the main vegetable products. Clearly the potassium dichromate is providing the chrome salt. Pyrogallol complexes have good longer term stability due to buffering however catechols suffer badly from instability in acid environments. There are also other mineral tannages for high stability; aluminium oxide (16 % Al2O3, ca. 50 % basicity).
    Compared to potassium dichromate, this could be considered "nice" - Aluminium oxide was taken off the United States Environmental Protection Agency's chemicals lists in 1988.

    So Gerry or PE, do you think that it may be feasible to replace the tanning action of the potassium dichromate with basified aluminium oxide?
    I haven't done any Bromoil work, but have seriously thought about trying it. This might make the route more available in the near future?

    Dave

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