Weird Mark on $200 Coin

Discussion in 'Gold Coins' started by SilverDJ, Sep 13, 2016.

  1. SilverDJ

    SilverDJ Well-Known Member

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    I got this $200 1992 gold coin and it has an unusual mark around the edge, that looks like some sort of tarnish?
    [​IMG]

    Excuse the stray fibre:
    [​IMG]

    Anyone got any clue what it is?
    I have no reason to believe the coin is a fake (if such things exist?)
     
  2. Jislizard

    Jislizard Well-Known Member Silver Stacker

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  3. SteveS

    SteveS Member

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    It looks very much like the mark left behind by the connector clip used when electropolishing, to me. Does it appear on the other side, too?

    I used to electropolish stainless steel components used in building mass spectrometer ion sources, and it often left marks like that. I can't imagine why you would electropolish a gold coin though :/
     
  4. SilverDJ

    SilverDJ Well-Known Member

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    No, just the one side.
     
  5. SilverDJ

    SilverDJ Well-Known Member

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    Yes, the $200 coins are 22kt, not sure what the rest is made of.
     
  6. Silver Soul

    Silver Soul Well-Known Member Silver Stacker

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    Spots like that are generally copper. However that mark looks like rust to me
     
  7. Aureus

    Aureus Active Member Silver Stacker

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    yep, just a copper spot which is completely normal.

    Perfect world the alloy completely blended with the gold, but when you get microscopic flecks that aren't (and happen to be on the surface of the coin) they oxidise over time. Some people avoid coins with copper spots and other numi collectors look at them as a sign of authenticity. Infact copper spots don't have any effect on NGC grading provided they aren't eroded to the point of damaging the surface.
     
  8. SilverDJ

    SilverDJ Well-Known Member

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    Thanks. Copper it is.
     
  9. Jislizard

    Jislizard Well-Known Member Silver Stacker

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    Nitric acid will dissolve the copper and leave the gold if it bothers you.
     

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