Preserving Metal Coins

The main agents of deterioration are corrosion, excessive humidity, temperature, air pollution, improper handling, carelessness, and water damage during a natural disaster, such as a hurricane, according to the American Institute for Conservation of Historic and Artistic Works (AIC).

 

Corrosion occurs from exposure to various gases, contact with water, heavy metal cleaners, or metals rubbing against each other. For example, silver and gold, which are noble metals, experience less corrosion than weaker metallic elements, such as tin, copper, lead, and iron. Excessive humidity, temperature fluctuations, and air pollution have irreversible effects on metal coins.

 

For example, dust particles and various chemical vapors can settle on the coins' surfaces and attract condensation, leading to corrosion, according to an article in "Archival Elements," the newsletter of the Science, Technology, and Healthcare Roundtable of the Society of American Archivists and the AIC's webpage on protecting metal objects.

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Although silver coins can tarnish and corrode in harsh environments, such as archaeological digs, they usually withstand erosion. However, coins comprised of silver and copper alloys experience corrosion more easily in harsher environments.

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Improper handling and carelessness by people accounts for much deterioration. Whenever people hold metal coins without wearing gloves, natural oils and acids are transferred from their skin onto the coins' surfaces, which leads to corrosion and pitting (corrosion that eats through the metal).

 

In addition, lackadaisical handling of metal coins has indelibly negative effects of breakage, dents, scratches, and bending. Similarly, using wire brushes for cleaning purposes is a terrible idea because vigorous scrubbing can destroy the coins' designs, plating, engravers' marks, and further damage the artifacts.