Here's what you need:

1/4 cup white vinegar (dilute acetic acid) 1 teaspoon salt (NaCl) 1 shallow, clear glass or plastic bowl (not metal) water measuring spoons paper towels

Directions:

1.Pour the salt and vinegar into the bowl. 2.Stir until the salt dissolves. 3.Dip a penny halfway into the liquid and hold it there for 10-20 seconds. Remove the penny from the liquid. What do you see? 4.Dump the rest of the pennies into the liquid. The cleaning action will be visible for several seconds. Leave the pennies in the liquid for 5 minutes. 5.Rinse the pennies and let dry.