Things You'll Need
1/4 cup vinegar
Two teaspoons salt
One tablespoon baking soda
Serious coin collectors do not clean coins, since in most cases, the cleaning job will lessen the coin's value. Most of the change in your pocket, however, is worth only the amount stamped on it. But cleaning pennies can be an interesting science experiment. Try cleaning some pennies minted before 1982 and some that were minted after, and see the difference. The pre-1982 pennies were made with more copper, and the chemical reaction is more intense.
Put two teaspoons of salt in a bowl. Pour 1/4 cup of vinegar into the bowl and stir until the salt is completely dissolved. Drop a handful of pennies into the bowl, making sure they do not touch each other. Let sit for five minutes. While the pennies are still in the bowl, scrub any remaining tarnish off with a soft toothbrush.
Remove the pennies from the bowl and rinse thoroughly in warm water. If you do not rinse completely, the vinegar and salt will cause the penny to be encrusted in a blue-green substance. The copper will react with the acetate in the vinegar and some sulfur in the air, causing the penny to be covered with blue copper sulfate and green copper acetate.
Create a paste with two parts baking soda to one part water. Use a microfiber cloth to rub the paste over the pennies. This will bring the shine back to the penny. Rinse the pennies thoroughly and dry them with a soft towel.