If the pennies are clean, but not shiny, mix a paste of baking soda and water and rub into the pennies. Wash it off and, tada!
If you don’t have vinegar, use lemon or even orange juice. Copper oxide (the gunk on your pennies) dissolves in weak acid, and that’s just what all three of these liquids are. [1] X Research source You can also use lemon juice instead of vinegar.
For those especially nasty pennies, scrub them with a scrubber or toothbrush after they’ve been resting in the solution for a bit.
If you don’t wash them off, a blue-green sheen will develop on your pennies. That’s what happens when the copper, oxygen, and chlorine (from the salt) combine (called malachite). [1] X Research source
After 1982, copper became too expensive to justify using on a coin just not worth anything. Therefore, zinc (a much cheaper metal) started being used.
