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WATER is one ENEMY of Copper COINs

If you look closely at the coins above, you will see all of the green and whitish corrosion that is most likely caused by water (among other things).  Over long periods of time, exposure of copper to water can result in corrosion caused by the interaction of the water itself but also in part do to the particles contained within the water. The following pictures show copper pipes in a home that have the exact same type of corrosion caused by pinhole leaks exposing the outside of the copper pipe to the water.

Example of water damage to copper pipe from pinhole leak that has dripped.

Example of water corrosion from a pinhole leak that has run along the copper pipe.

Example of corrosion where water has leaked from a coupler-fitting and collected on pipe.

Example of corrosion by water from a pinhole leak that has spread along the copper pipe.

Of course there are all kinds of other ways that our wonderful copper coins can be damaged, but a lot of the corroded pennies we encounter have either been exposed to water outside (laying on street or ground). Just remember that when it comes to water, the point is to keep your copper coins dry so when storing your copper coins, you need to ensure they are in a dry environment.

     U.S. Mint     American Numismatic Society     American Philatelic Society