Unlike most collectibles, coins are not values according to their shine. That is why once newbies ask experienced collectors how they can clean their coins to look their collection “look better,” the answer is almost always the same: “You don’t!”

Nothing reveals the true history and age of a coin, its unique character and value like the natural patina, and other aging and heavy circulation signs. And the same time, improper cleaning can instantly devalue and even destroy a coin turning a valuable collectible into another piece of metal.

In this article, we explain why cleaning can be dangerous for your coins and why the numismatic world does not consider cleanness as a reliable factor of coin evaluation.

It is not dirt; it is patina.

Before talking about why you should never try to clean your coins, let’s try to understand what that “dirt” is. This layer of toning that appears on a coin throughout time is called patina. In fact, it is not contamination but more of a metal’s natural protective mechanism. The patina creates a barrier covering a coin from the outer hazards, mechanic, and environmental damages.

Numismatists distinguish several types of patina:

• The patina of silver coins is usually dark grey or brown and becomes darker on the recessed parties of coins;
• Gold coins are usually most resistant to patina. Even the oldest golden items are known to numismatics usually acquire a light warm yellow-ish color with no signs of darkening or staining;
• Nickel coins usually acquire a dark grey patina that is much lighter on the protruding sections of a coin, making its relief exceptionally distinctive;
• Copper coins have either dark brown or green-is patina. The color usually depends on the fact that copper coins usually have other metal add-ons that alter the patina’s overall tone.

The color of the patina and its intensity depends on many factors. Humidity level at the storing place, circulation of the coin, climate, and air quality at the place where it has been minted, used, sold, and stored – all those can alter the patina of seemingly identical coins, making each genuinely unique.

How cleaning devalues a coin

The main reason why numismatics don’t want to deal with cleaned coins is that they are highly unprosperous if you look at them as a long-term investment. Once cleaned inappropriately, coins become highly fragile and vulnerable to other hazards.

One thing is to rinse a coin with water to remove some loose debris from it, and another is to use strong chemicals or mechanic cleaning. In this case, you have a solid chance to scratch a coin’s surface, removing fragments of metal from it. Many times amateur numismatics manage to entirely remove the upper layer of metal from a coin, turning a valuable collectible into a piece of metal.

The first known wave of improper coin cleaning and its consequences dates back to the 19^th century. Today you may find numerous coins on the market that date back to the early 1800s and may seem valuable but don’t attract serious collectors as they carry signs of scratching from rough abrasive cleaning visibly.

Once cleaned with abrasives like toothpaste, baking soda, and other DIY remedies, coins look pretty attractive in the beginning. But once one takes a magnifying glass, it instantly reveals ugly scratches and hairlines on the coin’s surface. They soon start to collect dirt and other contaminants altering coin’s relief and luster, turning it into a useless piece of metal.

Some consider chemical cleaning safer than abrasive methods. However, those who chose to clean their coins with strong chemicals such as acetone risk “overdip” a coin once they leave it in the solution for too long or don’t rinse the chemical off properly. In this case, a coin gets unnatural toning, the luster destroys irreparably, and this damage becomes permanent.

You may compare coins to collectible wine. Just like the noble drink, they get only better as time goes by, leaving its mark on them. “Not all that glitters is gold” – this old saying has almost a literal meaning in the numismatic world, and a true appreciator, a passionate collector, knows to see the true beauty of noble patina.