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  for Metal Finishing since 1989
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Green Copper

What makes copper green and how does it happen?

Max Glen
- Madison, Wisconsin, USA

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The "green copper" is actually copper oxide. This is the "rusted" form of copper. Copper reacts with oxygen in the air to form this green copper oxide. The chemists call this process a reduction/oxidization reaction. This reaction is encouraged by heat, water, and salt. Iron goes through the same type of reaction to form red iron oxide. Iron oxide is what most people think of as "rust."

Copper and iron form oxides because it is a more stable form. This is the same reason playing cards don't last forever in a card-castle form. Eventually, it gets knocked over and the cards in the "scattered on the table" form is much more stable.

Tim Neveau
Rochester Hills, Michigan