If your Lincoln Memorial penny has a date before 1982, it is made of 95% copper. If the date is 1983 or later, it is made of 97.5% zinc and plated with a thin copper coating. For pennies minted in 1982, when both copper and zinc cents were made, the safest and best way to tell their composition is to weigh them. Copper pennies weigh 3.11 grams, whereas the zinc pennies weigh only 2.5 grams. Be sure to use a scale that is accurate enough to detect the tenth of a gram (0.10) or better. If you weigh a zinc penny on a scale that can only register full 1 gram increments, the penny will usually display 3 grams, since the scale rounds the 2.5 gram zinc penny upwards to 3. The wrong type of scale can be misleading when you are trying to sort copper and zinc pennies.