Re: Why does copper turn your skin green?

Hi Jennifer,

You are right. It is indeed a chemical reaction that turns your skin green. What is happening on your finger is similar to what has happened to The Statue of Liberty over time. The Statue's 'skin' is made of copper sheets. As we know the Statue is not exactly 'copper' in color, rather it is green. This green layer on the copper is called the patina. The patina actually protects the copper from further corrosion. The patina forms, most favorably in damp air, when airborne sulfur compounds react with the copper. Copper(II)sulfate (CuSO₄) is a major component of the patina and has a green color.

To test for myself that copper sulfate could be responsible for your green finger, I placed one penny in a dilute solution of sulfuric acid (H₂SO₄) and another penny in water. I left them overnight and the next morning the penny in the acid had a green film on it, while the penny in the water had not changed. The sulfuric acid and copper had reacted to form copper sulfate.

Getting back to your finger, your perspiration creates an environment that is favorable for sulfur compounds in the air and in your skin to react with the copper to form copper sulfate. This is responsible for the green or blackish-green color.

For more information try out The Copper Page

Thanks for your question,

Cheers,

Scott Baginski
Dept. of Molecular Microbiology
in St. Louis