How To Clean Copper Pennies

If you've ever found yourself wondering how to clean copper pennies, you've come to the right place. Cleaning copper pennies can be a fun science experiment or can simply improve the look of your loose change.

To clean copper pennies, you will need:

• A non-metallic bowl
• Water
• A weak acid (such as vinegar or lemon juice)
• Salt
• Ketchup (optional)

1. Mix the ingredients. The first step to cleaning your copper pennies is to place the water, weak acid and salt into the non-metallic bowl. Note that using a metallic bowl can affect the removal of the copper oxide, which is what makes the copper pennies look dirty.
   
2. Add the pennies. Leave the pennies in the liquid for five to ten minutes. You can also hold one penny halfway in the liquid to see it change colors before your eyes. You might have to move the pennies around to make sure that all surfaces are cleaned.
3. Remove and rinse the pennies. This step is very important. When non-rinsed pennies soaked in the weak acid and salt solution contact the air, they can form a compound called malachite that will turn the pennies a blue-green color. After rinsing, lay the pennies out on a paper towel to dry.

If you don't have a weak acid and some salt on hand, you can clean copper pennies using ketchup. The vinegar and salt in the ketchup act in the same way as the vinegar and salt in the water solution. Just make sure to rinse the pennies extra well afterwards! Note also that pennies made after 1982 contain mostly zinc, and very little copper. Using these cleaning methods can be detrimental to the zinc in newer pennies. Do not attempt these cleaning methods on coins that have a value higher than their face value (for example, Indian head pennies) if you intend to sell them to a coin collector. Cleaning old, valuable coins can reduce their value.

Resources:

The Science Explorer