Copper: Why the Green?

Fernanda Sibilia "Confite" Patina CuffCopper can be gorgeous in its rosy untarnished hue but often doesn't stay that way.  Smudges, tarnish, oxidation and patina all change the look of copper if left untreated.  Ever noticed how anything copper that is left outside turns a bluish-green color in some places?  And also, with jewelry made of copper, sometimes it leaves a greenish mark on the skin?  

Fernanda Sibilia "Ceibo Hiluan" Mixed Metal EarringsSo why the green?  The reaction is between the natural acids, salt and moisture from skin + sweat combining with the copper.  Think about the patina (a surface reaction) that appears on copper roofs turning them this same frosty color.  This comes from the cupric acid naturally found in the metal which comes to the surface through oxidation (reacting with oxygen) and is triggered by moisture + salt.  This is the same reaction that happens on the skin due to natural perspiration.  

FYI:  The reaction of one individual to copper on their skin varies from person to person depending on the pH of the individual's skin.

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