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Coin Cleaning: How to Clean Coin Collections?

When we start collecting coins, the question of how to clean old coins and preserve them without damaging them over time immediately arises.

In this article we aim to give you as much information as possible so that you can make your own decisions, but you should bear in mind that you can damage the coin or lose its value, so we always recommend that you consult with your numismatist of trust.

When you start collecting coins, the question arises of how to clean old coins and preserve them without damaging them over time.

In this article we aim to give you as much information as possible so that you can make your own decisions.

What is the patina on a coin?

The patina in numismatics is a film that covers the coin and that forms on coins naturally with the passage of time and contact with the environment. When the coin goes further and suffers damage, we speak of corrosion.

Metals, with the exception of gold, undergo a chemical reaction when in contact with environmental agents such as air or humidity. This corrosion, which is nothing more than an oxidation of the metal, is produced by the loss of electrons from the atoms in favour of the amount of oxygen in the metal.

There are metals that are more prone to the formation of patinas such as bronze, copper or silver. In numismatics some coins with patina are highly valued if this patina is considered of good quality, this is because there are types of patina:

What is the patina on a coin?

Conservation of coins

For the conservation of coins we must take into account which are the main pollutants as we can prevent the deterioration of the pieces of our collection. There are products for handling, storing and preserving coins.

Air

It is important to store coins in containers that are as airtight as possible and to keep them away from contact with air. The main pollutant contained in the air is hydrogen sulphide and it reacts with the metals producing their oxidation.

Although some patinas are well considered in numismatics it is possible that if the process is not stopped the coin will deteriorate even more. The process is:

Humidity

Storing coins at a humidity of more than 40% causes deterioration. To preserve them properly, it is recommended to have an environment with a lower % of humidity than indicated and a moderate temperature.

The main cause of bronze cancer (unstable patina) is high humidity.

To control the humidity of collections, silica gel is used, which acts as a regulator of the environment.

Footprints

Our skin contains grease and elements that produce that if we handle the coins without gloves, especially the freshly cradled ones, these are marked with our fingerprints. These fingerprints over time will tend to produce a stain on the coin.

Footprints

The use of cotton or latex gloves is recommended for handling particularly delicate coins. If they have already been marked by a fingerprint, you can try to remove the stain with an eraser and alcohol.

Cleaning coins - yes or no?

Now that you know what patina is and the main causes of deterioration of coins, can old coins be cleaned? You will have already noticed the importance of patina, coins age and over time their surface creates a protective film due to the natural oxidation of the metal, if it is beautiful it has a great numismatic value. Good collectors appreciate the original appearance of a coin more than the artificial shine of a cleaned coin, that is why only buy coins whose appearance guarantees that they have not been cleaned before.

They will only buy coins whose appearance guarantees that they have not been cleaned before.

If you are still determined to clean them, here are some tips:

The best option for cleaning coins is to use a non-abrasive method, that is, one that preserves 100% of the coin material.

Cleaning old coins

Ancient coins such as Roman or Greek coins, even some more recent ones, are found underground and this usually requires cleaning in order to make their characteristics visible and to be catalogued afterwards. In many cases these remains of soil, clay and mineral aggregates are very difficult to remove without the use of mechanical methods such as brushes and points or even electrolysis.

Cleaning old coins

The first thing to do if you want to clean an old coin is to wash it with hot water and soap, rubbing it delicately with your fingers in circles.

Then, for coins made of materials such as bronze or silver, it is recommended to give them baths of olive oil or distilled water. It consists of leaving the coins submerged for 15 days, after which time they should be cleaned with soap and water and then submerged again. This process does not carry a very high risk.

Finally, there are different ways of finishing the cleaning process depending on each case and the condition of the coin, always taking extreme care not to damage the coins: