While this method should work on any penny, it's safe on the more recent ones, while the previous methods are not. The acidity of methods 1-4 will turn your zinc pennies black. 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.

How would you rephrase that briefly using Chinese?
找出一枚脏硬币和一块橡皮。