When does copper turn green?

Although copper is highly resistant to the chemical action of the atmosphere and sea water, it turns green if exposed to them for a long time. The color is caused by the formation of a thin coating of green basic copper carbonate known as patina or verdigris. The later name comes from the old French vert de Grece,  (green of Greece), but the reason for it is unknown. This beautiful green is often seen on copper roofs or statues, especially if they are near sea.

Copper was the first metal man learned to use. Five thousand years ago, when men discovered deposits of pure copper in what are now Iraq and Cyprus, they found that this fairly soft metal could be easily melted, cast in molds and hammered into tools, weapons and ornaments.

About half the copper produced today is used by electrical industry. Pure copper is the best cheap conductor of electricity and can be drawn into threads one-thousandth of an inch thick.