Dick Johnson submitted this entry from his Encyclopedia of Coin and Medal Terminology. Thanks. -Editor
Corrosion. In numismatics the advanced state of metal deterioration beyond tarnish. Iron coins rust, lead medals
form a white disease, tin and zinc objects erode, all under different chemical or environmental conditions. The best prevention for corrosion is to
lacquer the piece. While this is done for most medals, it is impractical for coins or blanks. The best protection for coins is to choose metal alloys
least liable to tarnish or corrode in most environments; these are, obviously, gold, silver and somewhat bronze.
Corrosion is the extensive tarnish or chemical reaction to a metal surface in a detrimental environment. Most coinage alloys tone or darken in
time, as copper or bronze ages; should coins and medals be exposed to harsher environment they may form tarnish. Should this detrimental condition
persist, it may become corrosion. Should a numismatic or medallic specimen reach this stage it is not worthy, perhaps, to be collectable. It is
assumed the detrimental condition is treated long before a specimen can be called corroded. See tone, toning; tarnish.
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Looking for the meaning of a numismatic word, or the description of a term? Try the Newman Numismatic Portal's Numismatic Dictionary at:
Or if you would like a printed copy of the complete Encyclopedia, it is available. There are 1,854 terms, on 678 pages, in The
Encyclopedia of Coin and Medal Technology. Even running two a week would require more than 19 years to publish them all. If you would like an
advance draft of this vital reference work it may be obtained from the author for your check of $50 sent postpaid. Dick Johnson, 139 Thompson Drive,
Torrington, CT 06790.
Wayne Homren, Editor
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