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What causes dark spotting like this on old Copper ?

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  • anablepanablep Posts: 5,096 ✭✭✭✭✭
    looks cleaned... maybe long ago...
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  • mgoodm3mgoodm3 Posts: 17,497 ✭✭✭


    << <i>looks cleaned... maybe long ago... >>




    That was my first thought, the color is wrong.
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  • originalisbestoriginalisbest Posts: 5,917 ✭✭✭✭
    Not just "looks" cleaned, but "is" harshly polished, and not worth your time. There are some coins you may not always be able to tell from a pic - this ain't one of 'em.
  • originalisbestoriginalisbest Posts: 5,917 ✭✭✭✭
    As for what causes that funk, a little moisture on that newly-brasso'd surface is more than enough. Yeeecchh.
  • airplanenutairplanenut Posts: 22,148 ✭✭✭✭✭
    That one's been terribly cleaned... that said, copper reacts nicely with carbon to create those ugly spots.
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  • darktonedarktone Posts: 8,437 ✭✭✭
    looks like it was dug up then cleaned.
  • cohodkcohodk Posts: 19,101 ✭✭✭✭✭
    Cleaning will cause spots like that.
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  • I am not sure what causes the black splotches, but they go actually into the surface of the coin even though they almost look like a thin coat of paint.
    So basically, the splotches aren't coming off without showing damage to the coin.
    The black splotches would actually be a impurity "like tin or zinc" in the copper planchette reacting with the envirommental chemcals.
    if it isn't too bad, you might be able to acetone clean the coin.
    Then stuff it in a raw potato for a while, acetone clean it again, use the darkener solution, and carry it around in your pocket for a year or so to age it back to almost
    normal.


    When I was a kid we used potatoes to power a small electric motor, nowadays they use one potato to power a little LCD clock.
    So I think the potato cleaning trick is actually a weak electrylosis cleaning system in effect.
    image

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