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Corrosion is a problem for most metals, though gold and platinum are nearly immune to its effects. A natural chemical reaction, it causes the surfaces of a coin to form new molecular compounds. Light corrosion results in the often pleasing condition of toning. When corrosion is severe or unattractive, it results in coins certifiable only under Details Grading. NGC’s graders may narrow down the problem area by using the terms OBV CORROSION, REV CORROSION and EDGE CORROSION.
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