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Need Help with 2007 Wash. $1 Black Finish

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  • #1

    Need Help with 2007 Wash. $1 Black Finish

    I don't know why this coin is so "black"...it is NOT 100% coverage, and, looks to be some type of toning..It is not paint, that's for sure...I googled sintered planchet, and got all kinds of pics...
    The rim has a crack that runs 100% around the entire rim, right down the middle, through all incused letters, numbers, if this means anything.
    Thanks for your thoughts...
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  • #2
    It looks like a sintered (improperly annealed) planchet.





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    This occurs when the coin spends too much time in the annealing process. Some folks feel it's caused from an improper alloy mixture which causes the darkening during annealing. There is an articale in the November 3rd, 2008 Coin World where collector/metallurgist Chris Pilliod stated "that an electron dispursive X-Ray examination of an affected coins surface (in this case a 2008 Monroe Dollar) show the dark bands to be manganese oxide." This opinion seems to fit except that it does not address similarly colored coins of the copper nickel alloys unless a certain amount of manganese is used for those alloys as well.

    Others feel that the darkening is due to copper dust being "sintered" to the planchets surface. Sintering is a process where metal particals are adhered to a metals surface using heat. Similar to the powder coating on some custom color wheels. ( The ISO definition of the term reads: “The thermal treatment of a powder or compact at a temperature below the melting point of the main constituent, for the purpose of increasing its strength by bonding together of the particles.”)

    BTW, this condition is not limited to the Presidential Dollars as it also occurs with copper-nickel clad coins and nickels struck during the late 50's. I've also encountered this on the 2004 Peace Medal Nickels.

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    Last edited by 19Lyds; 05-23-2010, 05:36 PM.
    Lee Lydston

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    • #3
      While the dark color may be due to improper annealing, this hasn't been proven. There are other causes of discoloration inside the Mint. The crack on the edge is due to the "hard upset" the planchet receives. In other words, it's not annealed before being sent through the upset mill.
      Mike Diamond. Error coin writer and researcher.

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