What Causes Coins to Rust?
Do Coins Rust? We have probably all seen pennies caked in a hard green dust. You may have assumed those coins were rusted. In fact, the only pennies that can truly rust are those manufactured in 1943. Traditionally, the U.S. Mint manufactured pennies from copper and zinc. Currently, pennies are made of 97.5 percent zinc with a copper-plating. But in 1943, during World War II, the United States government needed the copper from pennies for the war effort. So, for one year, the Mint struck pennies made from steel and coated them in zinc. Steel, also known as iron, is a necessary component for rust. The scientific term for rust is iron oxide. None of the other coins—nickels, dimes, quarters, half-dollars and dollars—contain steel or iron. As a result, coins cannot rust. But if that green dust on the penny isn’t rust, what is it? Oxidation Rust is iron oxide. Iron oxide is formed when the atoms in iron or steel and the atoms of oxygen in the air interact through a conducting liquid, us
