If you have a penny that was minted prior to 1982, it is made primarily of copper. According to online resource Copper.org, these pennies contained approximately 95 percent copper. These pennies were replaced by zinc alloy pennies after 1982, since the value of copper had greatly increased. Pennies tend to dull over time, which is natural for copper, since it is a reactive material. Fortunately, you can shine your pennies with household items and make them look brand new again.
Mix 1/4 cup of white vinegar with 1 tsp. of salt in a small bowl. Stir thoroughly until the salt dissolves.
Place the penny inside the bowl. If you are shining multiple pennies, only soak a few at a time, and make sure they are not touching each other. Allow the penny to soak in the solution for approximately five minutes.
Remove the penny from the solution, and use a soft-bristled toothbrush to gently remove any leftover grime.
Make a paste out of 1 tsp. baking soda mixed with 1 tsp. water. Use a microfiber cloth to rub a small amount of the paste into the penny.
Rinse the paste off of the penny with warm water, and set it on a clean towel to dry.