Old copper pennies can tarnish from water vapour and oxygen in the air. Tarnish appears as a green or black film on the pennies, and makes them look dull and dirty. Homemade solutions containing salt and mild acid cause the tarnish to loosen from the pennies, exposing the shiny copper underneath. Metal or brass cleaners can be used, as well. Clean your old copper pennies to restore their shiny, pinkish colour.
Fill a non-metal bowl with 1/4 cup white vinegar and one tsp salt. Stir the mixture with a spoon to dissolve the salt.
Place the pennies into the bowl. Allow them to sit for five minutes.
Remove the pennies from the bowl, and rinse them thoroughly with clean water.
Dry the pennies with a cloth. If tarnish remains, apply ketchup to an old toothbrush. Brush the pennies with the toothbrush and ketchup.
Rinse the pennies thoroughly with clean water to remove the ketchup.
Apply one tsp baking soda to a damp cloth, and wipe the pennies to restore shine.
Rinse the pennies with clean water, and dry them with a clean cloth.