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The E-Sylum: Volume 10, Number 6, February 11, 2007, Article 18 ON SILVERPLATING COPPER IN THE 1700S Regarding the question on silver coating a copper coin, Paul Schultz writes: "One possible method is currently called "immersion" plating. A silver salt is dissolved in water, and a piece of copper or other metal relatively more susceptible to corrosion is immersed. In what is called an exchange reaction, the silver ions are reduced to form a silver coating on the metal, while the metal substrate dissolves slightly (oxidizes) to provide the electrons for this oxidation/ reduction reaction. Thus, no electricity is needed. "Silver salts could have been created at the time by dissolving silver metal in an acid, and then neutralizing the acid with a base such as lye. However, the coating obtained this way is very thin and often poorly adherent. It would have worn off after the coin passed through only a few people's hands. Therefore, the thickness of the silver layer is important in determining how it was applied. "Less than a ten thousandth of an inch implies a chemical deposition such as immersion plating. More than 1 thousandth suggests a mechanical method, such as possibly placing a silver foil over the clean copper planchet before striking, or dipping the planchet in hot molten silver, or some other mechanical method. "Additional information can be obtained by examining the interface between the silver and copper layers, to find if they are distinct (cold bonding) or gradual (suggesting molten metal). A close technical examination of the coin is needed, and some tests might damage the coin." Wayne Homren, Editor The Numismatic Bibliomania Society is a non-profit organization promoting numismatic literature. See our web site at coinbooks.org. To submit items for publication in The E-Sylum, write to the Editor at this address: whomren@coinlibrary.com To subscribe go to: https://my.binhost.com/lists/listinfo/esylum | |
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