What is a good constant for cleaning pennies?

A good constant for cleaning pennies is a solution of equal parts vinegar and salt. The acetic acid in vinegar reacts with the copper oxide on the surface of the penny, while salt acts as an abrasive to help remove tarnish. After soaking the pennies in this solution for a few minutes, you can gently scrub them with a soft cloth or toothbrush for better results. Always rinse and dry the pennies thoroughly afterward to prevent further oxidation.