To clean your pennies you will need vinegar and salt. Use 1/4 cup vinegar to 1 teaspoon salt. Be sure to use a non-metal bowl. Mix the vinegar and salt, then add the pennies. It only takes a few seconds for them to get nice and shiny!
How does it do that?
Over time the copper on the pennies combines with the oxygen in the air to form copper oxide. It is the copper oxide that makes the pennies look dirty. The vinegar and salt creates an acid that dissolves the copper oxide. With the copper oxide removed, the pennies become nice and shiny.
How to Clean Your Dirty Pennies