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Have you ever wondered how to clean pennies? Cleaning copper pennies can be a lot of fun for kids! You can turn the coin from a dull brown to bright and shiny. Get out your tarnished coins & let’s get going!
I decided to turn this into science experiment with my kids to test a few different substances and see what works best to clean old coins.
I remember accidentally doing this one time with a packet of hot sauce from Taco Bell when I was in high school. That’s where this experiment idea came from! My friends & I thought it was so cool that the penny got so shiny.
Why Do Pennies Turn Brown?
Pennies are made of copper. When copper is exposed to oxygen it will corrode (turn brown) because of chemical reactions. The oxidation creates a brown coating called patina. These are copper oxide molecules and they actually protect the metal underneath. Over time, copper transitions from its shiny brown color to a darker brown shade. There are also layers of dirt and grime that build up on coins.
How to Clean Pennies:
If you are genuinely wanting to know how to clean pennies, I have learned that a mixture of vinegar and table salt will get them really clean and shiny. Soak them in the solution for a couple of minutes. Then gently scrub the pennies with a soft-bristled toothbrush. Obviously you’ll want to use an old toothbrush. 😉 Rinse the coins with warm water and use a soft towel to wipe them dry. Be careful not to create any scratches or abrasions on the surface of the coins as you clean them.
Why clean copper coins?
Coin collectors often want to clean coins. Collectible coins are typically displayed, so their owners want them looking good! You can clean your everyday coins, too if you want. But usually you only keep they for a short time. Rare coins need to be kept clean.
But for the sake of this experiment, we wanted to try some different substances to see what would work best for us. I let my kids help pick the different things to test.
We filled some cups with a small amount of different substances in our kitchen to see which one would get our dirty pennies the cleanest. I had my kids each take a guess at which thing would get the pennies the cleanest. They were way off, so it was fun to see which really did get them clean. We let the pennies soak for a time, then put them on a paper towel to dry. Next wipe or scrub the penny clean with paper towels.
Substances We Tested for Cleaning Pennies
When experimenting with how to clean pennies, we tested a variety of items, here are some ideas:
Lemon or lime juice
Water
Soy sauce
Dish soap
White vinegar
Ginger ale
Ketchup
Salt water
Hot Sauce
Mustard
Milk
Baking soda (we did not try this, but it would be a good option to add in!)
Pour a tablespoon or so of each substance in a a bowl, jar or cup, enough to cover the penny, then allow it to sit for a time. We left ours for 30 minutes.
Our Results:
We took them out and wiped each one off on a paper towel. You can see the surface of the pennies change and become shinier. You can then rinse them with soapy water and set them on a towel to dry. You may have to wipe off some of the built-up dirt on some of them.
Vinegar and lemon juice both work really well for cleaning pennies. But, ketchup was the clear winners for our pennies, with soy sauce next, maybe with a little more time they would have gotten a little bit cleaner.
This is a fun experiment to try with younger kids! My kids of all ages were interested in the results, though. So if you want to do it with older kids, just go deeper with the science!
Use myScientific Method Worksheetsto extend this!
See even moreSTEM projectsfor kids.
Now just for the sake of preserving history, here is our original image from the first time we tried this experiment about 10 years ago. 🙂
FAQs
Copper oxide dissolves in a mixture of weak acid and table salt-and vinegar is an acid. You could also clean your pennies with salt and lemon juice or orange juice, because those juices are acids, too.
What is the best thing to clean pennies with? ›
Ketchup contains vinegar and tomato acid, which can dissolve copper oxide. Simply apply a small amount of ketchup to the penny and rub it with a cloth or toothbrush for a few minutes. Rinse the penny with water and dry it off with a towel.
Which liquid will clean a penny better? ›
The acetic acid in vinegar dissolves these chemicals and leaves the copper surface of the penny looking shiny. Soap can clean lots of things, but it can't dissolve copper oxides. Younger kids: Do the experiment again with more pennies.
Why does lemon juice clean pennies the best? ›
Lemon juice contains citric acid, cola contains phosphoric acid, and vinegar contains acetic acid. The detergent and the water are not acidic at all. The acids in the lemon juice, the cola, and the vinegar react with the copper underneath the oxides on the outside of the penny to form new materials.
Does water or vinegar clean a penny better? ›
If you are genuinely wanting to know how to clean pennies, I have learned that a mixture of vinegar and table salt will get them really clean and shiny. Soak them in the solution for a couple of minutes.
How long does it take for Coca-cola to clean a penny? ›
STEP4 - Pop your coins into your glass of co*ke. STEP5 - Sit back and wait but you should be able to see a difference in the colour of your coins within about an hour.
What do professionals use to clean coins? ›
Ultrasonic Cleaners
These coins are cleaned by using distilled water with a small amount of detergent in a special vibrating container. Acid based cleaners will eat away at a coin's surface diminishing its value.
Is toothpaste good for cleaning pennies? ›
But these cleaners are often made with caustic chemicals that can do serious, and permanent, damage to a coin. Don't use toothpaste – Toothpaste is extremely abrasive. It can make your coins appear shiny, but cause significant damage to the surface.
Does ketchup clean pennies? ›
Ketchup contains vinegar, a weak acid, which breaks down the copper oxide on the surface of the penny. The salt in the ketchup goes on to add dissolved chloride ions to the mix. These ions bond with the copper, forming copper chloride. The copper chloride helps the vinegar further break down the copper oxide.
How does hydrogen peroxide clean pennies? ›
Has a cashier ever given you your change and you cringed at the grimy and oily feel of the coins? Hydrogen peroxide will fix that. Hydrogen peroxide will dissolve the years of dirt on the coins and sterilize them.
Household chemicals that can clean or discolour your pennies include baking soda, vinegar, ketchup, salsa, pickle juice, detergent, soap, fruit juice… the possibilities are limited only by your imagination.
How long does it take for lemon juice to clean a penny? ›
Bottled or fresh-squeezed lemon juice will work. Wait five minutes, then remove the penny from the lemon juice. The penny will get cleaner the longer it sits in the solution.
Does hydrogen peroxide clean pennies? ›
Yes, you can use hydrogen peroxide to clean coins. It can remove stains and tarnish and won't damage your coins' surface. However, it's best to use a diluted form of hydrogen peroxide instead of concentrated.
How do professionals clean coins? ›
The coin is dipped into a dilute acid solution that removes the oxidation from the coin along with a small amount of metal. Overdipped coins result in loss of luster which lowers the coin's grade and appeal. According to author Thomas E. Hudgeons Jr., this is the safest way commonly found coins are cleaned.
Why is ketchup good at cleaning pennies? ›
Ketchup contains vinegar, a weak acid, which breaks down the copper oxide on the surface of the penny. The salt in the ketchup goes on to add dissolved chloride ions to the mix. These ions bond with the copper, forming copper chloride. The copper chloride helps the vinegar further break down the copper oxide.
Does lime juice clean pennies? ›
Step 1: Chemical Eroding of the Coin.
Lemon and Lime juice are both acids. They erode whatever they come in contact with if given the proper amount of time. So don't leave your coin in the acid for more than 30 minutes or your coins major features will dissolve. Put the acid in the jar along with the coin.
