Aug 24, 2014

Beauty is skin deep, ugly goes to the bone

Dateless and partial date mis-struck Lincoln Cents are a common affordable entry point to error coin collecting.  With no visible date, one must look elsewhere to establish an age and value range.  Coin design provides solid clues, such as wheat ears marking the pre-1959 era.  Material composition is another distinguishing factor.  In 1982 the US Mint changed the metal composition of Lincoln Memorial Cents to reduce raw material cost.  Copper alloy (95% copper / 5% zinc) was replaced by a copper plated zinc core (2.5% copper and 97.5% zinc).  Direct weight measurement is a reliable way to tell the difference.  Zinc core cents weigh 2.50 grams nominal vs. 3.11 grams for copper.  

A weak aspect of zinc core cents is their distinct copper-zinc boundary layer, a construction resembling the first electrical battery invented by Alessandro Volta in 1800.  Volta’s battery used copper and zinc electrodes to produce an electric current in the presence of brine or vinegar.  Similar electrochemical reactions are possible when copper plated zinc core cents are exposed to atmospheric and handling contamination.  The zinc core becomes vulnerable when a strike error displaces copper plating.  Electrochemical reactions slowly degrade the coin’s appearance over time.  Due to the unsightly look and preservation challenges of exposed zinc core cents, many Lincoln Memorial Cent error collectors focus on pre-1983 copper only.  

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