Science Common Sense

196 - Why do some metals tarnish?

Some metals tarnish because they react with the air and other things around them. When this happens, a thin layer of a different material forms on the metal's surface, making it look dull and discolored. This is called tarnish.

For example, copper and silver metals can react with the air's oxygen and sulfur, making them look dull and discolored over time.