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  • Sara Thompson

Turn Copper Pennies Green

By Sara Thompson

Special to the Enterprise

Image credit is

St. Patrick’s Day might be over, but we can keep the green going with this simple home experiment.

Supplies: shallow bowl, pennies, white vinegar, salt, paper towels

Directions: Add about a ¼ Cup of vinegar to the shallow bowl, then add around a teaspoon of salt to the vinegar and mix until dissolved. Next place the pennies into the solution and let them sit for several minutes. Next, pull the pennies out of the solution and let them sit on a paper towel. Watch what happens. As the pennies rest on the paper towels, they will begin to get a green patina. This can take as little as an hour to up to several days to occur depending on the age and the cleanliness of the penny.

Explanation: Pennies are made from copper, which will form copper oxide when exposed to the air. This is what makes pennies turn a darker color as they age. The vinegar breaks up the copper oxide and exposed the pure copper underneath. As the penny dries it reacts to oxygen and salt creating the same green substance that made the State of Liberty what it is today.

Variations: There are many variations you can do with this experiment. You can use different acids instead of vinegar. You could make several batches and leave them soaking for different lengths of time. Try rinsing a few pennies before laying them on the towel to dry and see how that is different. Check to see if the date of the penny matters in how well the reaction goes. Pennies minted after 1982 are made of less than 3% copper and coated in zinc, how can this change the reaction?

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