Most people ask what type of juice cleans pennies because they or their child are performing a science experiment about the difference between acids and bases. The simple answer is that more acidic juices will clean pennies well and basic juices will have a much lesser effect. However, the simple answer is not particularly interesting. It is far more rewarding to find out exactly what works and what doesn't.
Basic Penny Science
All modern pennies have copper coating on the outside, and those dated before 1982 are made of pure copper. The copper comes in contact with the oxygen in the air and forms a chemical bond with it. The result is the compound, copper oxide. Copper oxide has a cloudy gray or green appearance which makes pennies look dirty over time. Soap and water will not wash this substance off because it is not water soluble. Instead, it is necessary to alter the chemical bonds by adding an acid to the mix. This acid reacts with the oxide and dissolves it from the penny's surface.
So What Type of Juice Cleans Pennies?
Some juices will have almost no effect on pennies, while others will clean off the copper oxide completely, revealing a shiny penny that looks just like new.
The best juice for cleaning pennies isn't really a juice at all. Pickle juice is actually a vinegar. The reason pickle juice cleans a penny so well is it contains acetic acid, which breaks down copper oxide. The clear second place is lemon juice. Those tart little lemons work to remove copper oxide because they contain citric acid. Since lemon juice has the highest concentration of citric acid of any fruit, it works the best. Other juices that rank highly include lime, grapefruit, and orange juice.
While they won't work as well as lemon and lime juice, other juices contain a moderate amount of citric acid. These include cranberry, grape, and other berry juices. Because they contain citric acid, these juices will work to break down copper oxide; however, the pennies will need to sit in the solutions longer. Additionally, while this juice might work well for one penny, it will take far longer to clean multiple pennies.
Just Don't Have It
Juices that won't work are those considered alkaline. These include juices like apple and peach, which don't contain citric acid so they will not have any effect on copper oxide.
How to Clean Your Pennies
When you are cleaning your pennies, use highly concentrated or freshly squeezed juices. These won't be watered down and will react more quickly. You also need a container to clean the pennies in. If you have many pennies, use a glass jar such as a gallon mason jar. For just a penny or two, use a cup or mug.
- Put the pennies in the container.
- Add the juice. Pickle or lemon juice works best.
- Let the pennies sit. (The time will vary based on the oxidation and the number of pennies. This could take a few hours to days.)
- If you have a lot of pennies, shake the jar a few times a day to make sure the juice covers all of them.
- After all the copper oxide is gone, use a strainer to drain the juice. However, don't throw away your juice in case some still need it.
- Rinse with cool water.
- If any pennies still have oxidation, put them back in the juice.
How to Test
Since it's always more fun to find out firsthand than to read an article, why not conduct an experiment? All you need is about a cup of each of the above juices, a mason jar for each juice, pH paper, and 18 oxidized pennies. Try to select pennies with similar levels of oxidation.
Once the materials are ready, follow these steps:
- Pour each juice into a mason jar and label it with tape.
- Dip a piece of pH paper into each jar. The bluer it turns, the more alkaline the juice. The redder it turns, the more acidic. Set the papers aside to dry and label each.
- Drop two pennies into each jar and seal it tightly.
- Let the pennies sit in their respective juices overnight. Refrigerating the jars is optional.
- Check the results the next day and compare them to each juice's pH.
- Rank the appearance of each penny from one to five and see how it corresponds to acidity.
Also known as litmus strips, pH paper is treated with a substance capable of distinguishing acidity. It's available at stores that sell scientific supplies. You can also order litmus strips online.
After figuring out what type of juice cleans pennies, pull the pennies out of the jars, rinse them under warm water, and set them on a paper towel to dry. Then, glue the pennies and the corresponding PH paper to a board to present the results to others.
While this experiment is a good way to teach kids about chemistry, it is not a good way to clean pennies that are collector's items. In fact, cleaning old coins in any way can severely reduce their sale value. A better thing to do in this situation is to take the pennies to a professional restorer. This person may be able to "fix" the pennies without changing their chemical makeup.