Why is the Statue of Liberty green?

When the Statue of Liberty was dedicated in 1886, its copper skin, only about 2.4 millimetres thick, was a shiny reddish-brown like a new penny. Exposure to oxygen, water, carbon dioxide and sulphur pollution caused a series of chemical reactions, forming copper carbonates, sulphates and chlorides. By around 1906 the statue had turned mostly green. This patina, also called verdigris, protects the copper underneath from further corrosion. Officials considered painting it in 1906, but public opposition helped keep the green colour that is now iconic.