This Is What the Blue Stuff Is on Coins

Collecting coins is all fun and games until you realize some of them have blue stuff on them. The blue stuff that develops on coins can significantly impact their appearance and value over time, so you’re probably wondering what it is and how to get rid of it.

The blue stuff on coins is usually a sign of corrosion on the metal, which is common with coins. Corrosion occurs when the metal interacts with the oxygen and moisture in its surroundings, so you should keep your coins dry. 

Understanding the blue stuff on coins is important if you’re an avid collector. This article will discuss why corrosion occurs, how to deal with it, and how to store your coins in a way that prevents corrosion.

Why Do Coins Corrode?

Coins corrode because they’re made of different metals, like nickel and copper. Unfortunately, these metals are susceptible to green and blueish growths due to corrosion, which is more likely to occur in a wet or humid environment.

It’s not just moisture and the air (oxygen) that causes coins to corrode and turn blue. There are other things to be aware of, including:

  • PVC coin holders
  • Hydrogen
  • Electrical currents
  • Dirt and bacteria

So, if your collector coins interact with any of the above, they’re more likely to corrode over time.

Small amounts of corrosion on a coin shouldn’t cause much of an issue, but a coin with many blue and green growths can look undesirable and lose value. Therefore, you must keep your coins in a dry environment, away from things like dirt and PVC (especially if they’re particularly valuable).

Old Coins Are Most Likely To Corrode

Many coins have been around for decades or even centuries in some cases. As you can imagine, these coins have gone through many people’s purses and hands and come into contact with all kinds of things, including dirt, grime, dust, moisture, and so on.

Due to the history of most old coins, they’re more likely to become blue and corroded over time, and there’s not much you can do about it. Even then, ensure you store them in a secure and dry place, which will reduce the rate of corrosion and avoid corrosion as a result of contact with water. 

How To Clean Corroded Coins

There’s a way to remove corrosion from coins, but it’s not always the best option. Having a coin collection evaluated before cleaning is a good idea. In the case of valuable coins, cleaning is best avoided because it can significantly devalue them.

Below is a guide on cleaning corroded coins that have turned blue over time:

  1. Place the corroded coins in a container. 
  2. Pour white vinegar in, ensuring it covers all coins. 
  3. Leave the coins to soak for a few hours (overnight if they’re extremely blue and corroded). 
  4. Remove the coins from the container and scrub them using a small brush. 
  5. Rinse the coins in water. 
  6. Dry the coins using a clean cloth. 

White vinegar effectively removes corrosion stains due to its acidity, so your coin collection should look much cleaner afterwards. However, it can also wear away the coin’s coating, affecting its appearance and value. Ensure you’re okay with this possibility before soaking anything in white vinegar!

Other products that can fix coin corrosion include acetone and baking soda.

How To Prevent Coins From Corroding

It’s frustrating when a coin collection corrodes because it can seriously affect the appearance of each piece. Thankfully, there are plenty of simple things you can do to ensure coins remain corrosion-free, and below is a list of the main things.

Keep the Coins in a Dry Environment

Humidity can speed up the corrosion process and is highly problematic if you have a valuable coin collection. Just like when you leave a bike out in the rain for too long, and it begins to rust, a coin will corrode when exposed to moisture. 

Never store coins outdoors or in areas that are damper than others. For example, a garage is usually not an appropriate place to store collector coins unless it’s well-insulated and dry.

Avoid Placing Coins in Direct Contact With Each Other

When coins are placed in direct contact with each other, they might get scratched and damaged. It’s also harder to examine coins if they’re bunched up on top of one another, so you might miss problems like corrosion. Over time, the corrosion could get worse without you even realizing it.

It’s always best to store coins in a place where they each have their own space and are visible so you can examine them from time to time and stop issues like corrosion while you can. 

Keep Coins Sealed in a Hard Container

Coins corrode when they come into contact with the air and moisture in their environment. So, keeping them sealed in a hard container is an excellent way to prevent corrosion because it blocks oxygen from getting in and interacting with the metal.

When choosing a container, be sure to go with one that doesn’t contain PVC as it can make corrosion worse and leave blue/green stains on coins. Many hard plastic coin holders are appropriate because they don’t contain PVC, and they protect the coins from damage and too much oxygen and moisture.

Avoid Touching the Coins Too Frequently

Another tip is to avoid touching the coins too much. Your hands might have harmful materials and chemicals on them without you realizing it. If you touch your coins while your hands aren’t clean, it could cause further corrosion.

Also, touching coins often means you’ll have to remove them from their packaging and expose them to the air and atmosphere, which can be problematic over long periods.

Only touch the coins if necessary to ensure they remain in good condition and prevent them from turning blue or green!

Does Coin Corrosion Get Worse if Not Treated?

In most cases, coin corrosion will get worse if not treated, especially if you don’t remove the coins from the environment that caused the corrosion in the first place. The blue stuff can continue to degrade and destroy the coin, eventually making it devalued and worthless. 

As the corrosion develops, the coin also begins to look less desirable. Corrosion can ruin the appearance of the most beautiful and interesting coins, so you must act fast if you notice your collection turning blue or green

One of the best ways to treat coin corrosion is to figure out the most likely cause and start from there. For example, if you’ve been storing your coins in a soft plastic PVC container and are beginning to notice blue stuff forming, now is the time to switch to a non-PVC container.

Should I Leave the Blue Stuff on My Coin?

You should leave the blue stuff on your coin if it’s valuable because cleaning could potentially damage and devalue it. However, if the coin isn’t too valuable or you don’t mind risking some scratches and other damage, cleaning it off is a good idea.

In the case of a low-value coin, cleaning isn’t always worth the hassle. Consider whether it would be better to buy a new coin or collection rather than trying to salvage one that’s already highly corroded. 

Another good reason to leave the blue stuff on coins is so that you don’t accidentally spend them! Check out my other article to find out why accidentally spending your collector’s coins could be a bad idea: Can You Spend Collector Coins Like Normal Money?

Why Does PVC Cause Coin Corrosion?

PVC causes coin corrosion because it contains hydrochloric acid, which reacts with moisture and oxygen to create pesky blue and green stains. Many people who store their coins in PVC containers don’t realize the negative impact they can have over time, which is why they end up having to dispose of them.

Do All Coins Corrode Over Time?

Unfortunately, most coins corrode over time because of their interaction with oxygen. Since oxygen is everywhere, it’s challenging to keep coins away from it, especially if they were once in circulation. 

And as oxygen is one of the leading causes of coin corrosion, it’s no surprise that most coins will experience some level of corrosion after a while.

Copper oxide, a form of corrosion, commonly appears on coins over time due to the metal interacting with the atmosphere. 

Should You Keep Corroded Coins?

Whether you should keep corroded coins depends on the circumstances. If it’s a highly valuable or meaningful coin with just a small amount of corrosion, you should keep it. However, if it’s highly corroded to the point where you can barely make out what it is, it might not be worth keeping.

If you’re still unsure, have the coins evaluated by a professional to determine the best solution.


The blue stuff on coins is corrosion, which occurs when metal interacts with the atmosphere and moisture or when you store coins in PVC containers. After reading this article, you should have a better understanding of what to do if your coins are starting to corrode.

While the blue stuff is undesirable, it’s not always a good idea to get rid of it, especially if you have valuable coins. 

And while corrosion is inevitable in most cases, you can delay it by storing your coins the right way.

Alexander Picot

Alexander Picot is the principal creator of, a website dedicated to tips on finding and collecting precious items. Inspired by reading countless adventurer reports from the oldtimers, Alex is passionate about discovering hidden treasures and loves to share his experience with the rest of the world.

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