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

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