When France gave America the Statue of Liberty—a gift that commemorated the country’s struggle for independence and democracy—the monument was a shiny copper. But as the decades passed, Lady Liberty’s look evolved: First, the statue dulled to brown, and then she faded to her signature blue-green hue.

The culprit? A series of unique, interconnected chemical reactions, which resulted in a mixture of minerals. These compounds are responsible for the Statue of Liberty’s present-day shade.

Learn the exact science behind Lady Liberty’s look by watching The American Chemical Society's latest Reactions video, below.