Red-gold and gleaming, copper bracelets have long been popular jewelry items in nearly every culture. Copper bands, bangles and chains can retain the rich color of the metal if you understand why the copper changes color and how you can prevent it.
Copper changes color when it is exposed to air and moisture, much like iron rusts when it is exposed to the same elements. This natural process is called oxidation.
The chemical reaction between copper, oxygen and airborne sulfur creates a film of copper oxide and copper sulfide on the surface of the bracelet. As the film gets thicker, the color of the copper darkens slowly from orange-red to brown, black and eventually bluish-green. You may hear the greenish color of oxidized copper referred to as “patina.”
It may take several months of regular exposure to the elements for a copper bracelet to show visible color change. It may change color more quickly if the air is high in moisture or if there is a high concentration of sulfur in the air.
You can keep your copper jewelry from changing color by coating the metal with a clear lacquer or with a thin coat of clear nail polish.
Restoring Copper Color
Robyn A. Harton at CrystalsandJewelry.com recommends cleaning tarnished or discolored copper bracelets by soaking them in Worcestershire sauce for a few minutes.
References and ResourcesCorrosionist: Why Does Copper Turn Green?
CrystalsandJewelry.com: Cleaning Copper Jewelry
Chemistry Comes Alive!: Oxidation and Reduction of Copper
Copper.org: Copper Weathering Chart