How to clean dirty pennies

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.

Vinegar (or Lemon Juice) and Salt

This method is the best way to clean your pennies, and it will produce a very bright orangey-copper color on your pennies. It does this by using the low levels of acids that are contained naturally in vinegar and lemon juice to remove the patina (brown oxidation) on the penny.

Vinegar and Salt

Make a solution of vinegar and salt and let the pennies soak. The acid in vinegar, like in citrus, is what really takes the tarnish away.

You can see the surface of the pennies change and become shinier. You can then rinse them with running water and set them on a towel to dry. Vinegar and lemon juice both work really well for cleaning pennies.

All pennies start out the same color—bright copper. But somewhere along the way, those pennies lose their luster. The negatively charged oxygen atoms in our air are attracted to the positively charged copper atoms in the penny. When oxygen binds with copper, they form a new molecule known as copper oxide.

The copper in a penny, whether it forms the bulk of the coin or merely a surface layer, turns dull when exposed to the air. The reason is that copper atoms combine with oxygen molecules to form copper oxide, in a chemical process called oxidation.

When copper is exposed to oxygen, it forms molecules called copper oxide that make pennies look dirty. Pouring vinegar over the pennies helps break up this copper oxide and expose the pure copper on the penny. As the penny dries and is exposed to the air, a chemical reaction occurs and the penny turns green!

In general, old coins should not be cleaned. While you might think that getting all the years of dirt and grime off a coin would make it more valuable, the opposite is actually true! By cleaning a coin, you may actually damage it and decrease its value. At worst, you could permanently damage the coin.

Pennies are largely made of copper, which means they oxidize just like many other metals. However, rather than rusting, pennies simply get covered in a coating of green that can be polished off. Turning a penny green does not eat holes into the penny.

GREEN PENNIES AND THE STATUE OF LIBERTY

Your green pennies have what is called a patina. A patina is a thin layer that has formed on the surface of your copper penny from “weathering” and oxidization from the chemical process we just put the penny through.

There are several methods available for reverting green pennies back to their former shiny copper glory. To clean about two dozen, stir ¼ cup of white vinegar and 1 teaspoon of salt until the salt dissolves in a non-metallic bowl. Soak the pennies in the mixture for five minutes.

Copper oxide dissolves in water, but it usually takes a long time. The combination of vinegar (a weak solution of acetic acid), and table salt (sodium chloride) helps to dissolve the copper oxide, and also forms the blue copper(II) ion, which is soluble in water. The penny becomes shiny again!

In mid-1982, the coin’s composition was changed again, this time to copper-plated zinc. The last mostly-copper cents (95% copper metal composition) were produced by the Denver Mint on October 22, 1982. The copper-plated zinc cent coins are still being produced today.

Copper Pennies Are Worth More Than Face Value

In general, all pennies made before 1982 have a composition of 95% copper and 5% tin and zinc – with the exception that during some of those years, there was no tin in the alloy. Also, there was the steel 1943 Lincoln cent (and 1944 steel pennies, which were made in error).

It’s true — there’s a rare 1983 copper penny (specifically, a 1983-D penny) that’s worth $15,000. It’s a coin that many numismatic experts (those who study coins) still don’t fully understand — because it’s unlike any other copper penny the United States Mint has ever made.

1. You want to focus on hoarding pre–1982 U.S. pennies, which contain 95% copper content, making the coin at least twice as valuable as its 1 cent face value. (Post-1982 pennies are not worth collecting, as they contain only 2.5% copper content — the rest is zinc.