What Causes the ‘Rust’ on Coins Over Time?

Coins turn rusty because they react with air and water over time. Imagine the coin is like a hungry person, it wants to eat oxygen from the air, and when there’s water around, it eats even more. This makes the coin change color and feel rougher.

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Examples

  1. A copper penny left on a windowsill turns green after months in the sun.
  2. Coins in your piggy bank may look dull if they are left there for years.
  3. Old coins in your wallet might have a rough texture from oxidation.

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Categories: Science · chemistry· oxidation· coins