In this video we clean pennies with vinegar and salt.
Just mix together some vinegar with enough salt to make a saturated solution. The apply the solution to your tarnished pennies. The combination of acid and chloride etches the tarnish away to reveal the clean copper underneath.
Don’t leave the acid on or it will keep etching and produce an ugly green coating of copper salts. So wash off the acids with water after the pennies are clean.