The Statue of Liberty was originally the color of a shiny new penny.

When it was unveiled in New York Harbor in 1886, the Statue of Liberty was a dull brown-orange, the natural color of the 100-plus tons of copper sheeting used to build its skin. The green patina familiar today didn’t appear until decades later, as the copper reacted with oxygen, carbon dioxide, and moisture in the air to form a stable layer of copper carbonate.

The color change happened gradually over roughly 30 years and was largely complete by the 1920s. Far from being a sign of damage, that green patina actually protects the copper underneath from corroding further, which is one reason the statue’s skin, less than the thickness of two pennies, has held up for well over a century of coastal weather.