There is no more iconic figure of New York City than the Statue of Liberty, replicated in any souvenir you can think of, however, the blue-green hue that maybe has come to your mind has not always been the statue’s color. In the beginning, it had a copper color and changed over time to a turquoise hue, but why? Well, the answer relies on basic chemistry.
Lady Liberty’s statue contains thirty tonnes of copper, enough to make 435 million one-cent coins and the copper used to make the statue is one of the finest qualities. This is the main reason it changed color, the blue-green color it has nowadays is a result of oxidation.
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The origins of the Statue of Liberty
The statue arrive in the United States in 1886 as a gift from a French copper magnate named Pierre-Eugène Secrètan. It was entirely made of high-quality copper from one of his mines and was entirely built in France.
At the time of its unveiling, the statue had a shiny brownish color, just like a brand new penny. However, as time passed by, it began changing its color, first to a darker brown and later to the world-renowned “Liberty Green”. But how did it happen?
Why did the Statue of Liberty change color?
It all can be explained with a little science. Twenty years after the unveiling of the statue, it began to be covered with a green patina, a thin layer of oxidation that covers copper and bronze and can preserve metal for centuries.
The first color change, into a darker hue, occurred when the copper started reacting to oxygen in the air. This led to an exchange of electrons between copper and oxygen causing a pinkish red. As more and more electrons were exchanged, they began forming tenorite, which is black and which cause the statue to have a darker color.
However, oxygen is not the only element in the formula that led to a change in color, but pollution and acid rain as well. When the copper started to interact with sulfuric acid, due to the pollution in the air, it began to turn green.
To add an extra, the chloride from sea spray made it even greener, and as a result a very distinctive and almost exclusive turquoise color often referred to as “Liberty Green”.
This very same reaction happens to coins and even some of the skyscrapers in New York City.
What can be done to stop it?
When the process of oxidation and the changing of color began, New York authorities planned to paint the statue back to its original color, however, new Yorkers were against that decision so it has stayed green since around 1920.
However, it the patina that covers the statue is removed, a beautiful copper tone remains underneath. Something that probably, we will never see again.
