Why is the Statue of Liberty green?

The Statue of Liberty is green because it is covered in copper, and copper reacts with air and moisture over time to form a green surface layer called a patina. When the statue was completed and dedicated in 1886, it was not green at all, it was the shiny reddish-brown of a new copper penny, and it stayed coppery for years before slowly changing color. Over roughly two decades, exposure to air, rain, and the salty, humid harbor environment oxidized the copper skin, and by around the 1900s to 1920s it had weathered to the pale green (technically a mix of copper compounds) we know today.

The chemistry is the same process that tarnishes a penny or turns old copper roofs and church domes green: copper reacts with oxygen, water, carbon dioxide, and, near the sea, salt, forming copper carbonate and related compounds in that distinctive verdigris green. Crucially, this patina is not damage in the harmful sense; it actually forms a protective coating that shields the copper underneath from further corrosion, which is part of why the statue's thin copper skin has survived so well for well over a century. When the statue was restored in the 1980s, officials specifically chose to preserve the green patina rather than strip it back to shiny copper, both because people had come to love the color and because the patina protects the metal. So the green is copper doing what copper does, a slow, natural, and ultimately protective transformation from the gleaming brown gift France sent in 1886.