Why do rings turn your fingers green?

Answer 1

Cheap copper rings do this its the same reason as the Statue of Liberty
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Your fingers are turning green because the metal in your ring is reacting with the acids in your skin to form verdigris (metal salts). In order to avoid this you should obtain jewelry made form pure silver, gold, platinum or stainless steel. A word of caution, your body can become allergic to the metal salts (particularly nickel and chromium) and give you bad allergic rashes.