Why does copper turn green?

Why does copper change color and turn green over time? When copper is left outdoors it corrodes, then forms a pale green coating called a patina that protects it.

It is something similar to what happens with iron. When iron is left out in the open, a flaky orange coating forms around it. In the case of copper, the color of the layer or patina is green.

Patina is actually good for copper, protecting it from further corrosion . In fact, it works as a waterproofing agent. For example, it is very common to see the roofs of old buildings bright green.

The Statue of Liberty is one of the most notable examples of how patina preserves copper . Over the past century, weathering and oxidation have caused the statue’s encasing copper to shrink, but only 0.005 inches. Actually, the patina has protected him all this time.

At first the Statue of Liberty had a reddish-brown color. But over the years it changed color to a bluish green, as the patina formed on the surface. This is how one of the icons of the United States changed color. Here more curious facts about the Statue of Liberty .

In addition to natural formation, did you know that there is artificial patina? Artificial patina is nothing more than chemical solutions that, when applied to copper or bronze, react to form a thin layer of colored corrosion. Artificial patina is often used on sculptures to give them an antique feel.

The next time you see some green on copper, remember that green coating is protecting the copper from corrosion.

Isn’t it amazing how chemical elements work? 

Article published in planetacurioso.com.