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There are three categories of error coins as provided by the American Numismatic Association. Metal usage and striking errors referred to widely as “planchet errors”, die errors, and mint striking errors. This does not include the varieties that the US Mint has issued over the years. Since the inception of coin collecting there has been much controversy over what constitutes a true mint error. An organization of coin collectors named the Combined Organizations of Numismatic Error Collectors of America (CONECA) was created that specifically deals with mint errors. == Planchet Errors == A planchet is produced by punching blanks in sheet metal stock specially made for the types of mint blanks required. After the blanks are punched they are rolled on the edge placing an upset needed for the minting process. The blanks are then washed and annealed making them ready for the minting process There are several types of planchet errors that include: improper alloy, wrong stock, imperfect blank, and lamination. A planchet error may be caused by an improper alloy mixture. Improper alloy mixtures occur when the sheet stock contains uneven layers of the metals intended for the type of coin that is produced. A result of improper layers of metals is a coin produced without an intended surface layer of nickel. A dime or quarter without the nickel layer will contain only the copper alloy mixture. A planchet error can be caused by using a blank intended for a different denomination or wrong stock. The result of using a blank intended for another denomination is the minting of the intended obverse and reverse on the wrong stock. A planchet error also refers to many types of issues where an imperfect blank has been used. Pieces of the blank might be missing causing a half moon to be missing from the coin. Collectors denote missing parts of the planchet as "clipped planchets." A dirty or oily blank may cause the details of the coin to become dull or even missing. A piece of debris may find its way into the dies causing a series of lines to be minted on the surface of the coin. A planchet may be in a state that causes peeling on the surface of the coin. The peeling of any part of the surface of a coin is known as a lamination error. Below is a lamination error on a Jefferson nickel. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「US Error Coins」の詳細全文を読む スポンサード リンク
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