Every numismatist has faced the question at least once: should a coin be cleaned and years of accumulated dirt and oxides removed or not? This article does not offer a simple answer, because in the numismatic world there is a deep division of opinion. On one hand, there is the fear of losing the coin's value, while on the other hand, cleaning can contribute to a better appearance and visibility of details. We will consider arguments from all sides and present common methods used in this delicate process.
Arguments for cleaning
Cleaning coins can be useful in certain situations. For example, removing surface dirt or oxides can help identify coins that are otherwise unreadable. Also, mild cleaning can improve the aesthetic appearance of coins that are of no special numismatic value, but have sentimental value to the collector. Although they might (strictly speaking) lose market value, they will look „nicer.“ However, it is very important here to proceed with caution and use those cleaning methods that are less aggressive so as not to cause permanent damage.
By the way, it used to be common to clean coins, as numismatic experts themselves recommended it. Various cleaning methods were used; ranging from erasers to wire brushes and potassium cyanide, all with the goal of making the coin look shiny again. However, along with the introduction of certified grading (quality assessment) which emerged in the mid-1980s, the practice of cleaning coins began to decline. Most experts have since begun to speak out against cleaning coins, as it can negatively affect their grade and market value. If a potentially valuable coin absolutely must be cleaned (for example, it is completely coated in oxide), then professional cleaning is recommended. This is especially true for ancient coins, which are almost always cleaned.
Arguments against cleaning
Most of today's numismatic experts agree that cleaning coins can do more harm than good. Cleaning can remove the original patina that gives a coin its „natural“ look and often reduces its market value. Even methods that seem harmless can cause microscopic scratches on the surface, known as „hairlines,“ which can significantly affect the coin's grade of preservation and overall value. Therefore, experienced collectors and numismatists usually advise leaving coins in their original condition. It should certainly be kept in mind here that the preservation of a coin is generally judged by the state of the relief—that is, how worn the relief is—rather than by its „shine.“ A coin with a perfectly preserved relief is treated as a perfectly preserved specimen, regardless of the fact that, for example, it „does not shine.“ This is often the case with bronze specimens.
Common coin cleaning methods
There are various cleaning methods used, some of which are traditional and some more modern. One of the gentlest is the use of mild soapy water and a soft brush, but even this can be risky. Other methods include using baking soda, olive oil, or even electrolytic cleaning for specific types of coins. However, each of these methods can have its drawbacks, and it is important to be thoroughly informed before attempting any cleaning.
Use of abrasive agents
Using baking soda, granular cleaning agents, and even a pencil eraser cause damage to coins during cleaning. Brushing a coin with a toothbrush or a soft brush can create tiny scratches on the coin's surface. These scratches, known as „hairlines,“ can affect the grade of preservation.
Polishing
Aggressive cleaning that gives coins a very high, but „unnatural“ shine. Coins like this that „shine like a mirror“ are usually considered ruined. Also, polishing cannot turn an ordinary coin into a proof.
Cleaning with a cloth
Coins can sometimes be cleaned by gently rubbing them with a cloth, but it must be kept in mind that this causes the appearance of hairlines. This will not be noticeable on coins that are more heavily oxidized, but if it concerns coins that are still shiny, then it is noticeable.
Acid immersion
A coin is immersed in a dilute acid solution which removes oxidation from the coin along with a small amount of metal. This is a method often used for coins made of precious and some non-precious metals. If this method is skillfully applied, then it is sometimes difficult to notice that the coin has been cleaned. It is not recommended at all for bronze (copper) coins, because that results in a „red coin“ of a very unattractive appearance.
Washing with soap and water
This is the safest cleaning method, as it removes dirt and grease deposits from the coins. When cleaning, the use of distilled water is recommended, because tap water contains chlorine.
Cleaning with olive oil
A coin is immersed in olive oil, which, according to some, works best on common copper or bronze coins.
Cleaning with potassium cyanide
This solution was commonly used as a coin cleaning agent in the first half of the 20th century, and it sometimes led to fatalities due to poisoning.
Cleaning with ultrasonic cleaners
Coins are cleaned using distilled water with a small amount of detergent in a special vibrating container. Acid-based solutions should be avoided here, as they can corrode the coin's surface.
Cleaning with vinegar and salt
According to some opinions, washing coins with natural white vinegar and iodized salt in distilled water is a harmless way to clean coins.
Cleaning with a rotary brush
Coins are „cleaned“ using a high-speed rotating wire brush. This is strongly discouraged, as it severely damages the surface of the coins in this way.
Carefully consider your decision before cleaning
Before making a decision to clean coins, it is important to thoroughly research and consider all possible consequences. If you decide to clean them, it is recommended to first test the method on a less valuable coin. Always keep in mind that every coin has some value of its own, and by cleaning it, we may unintentionally diminish a part of that value. Also, keep in mind that shine does not immediately mean higher value. In numismatics, original luster is prized, and if it is not there, it cannot be artificially created.
Also, keep in mind that perhaps one day your collection will be sold. If you do not do so, your heirs might. If there are cleaned or improperly cleaned specimens in the collection, this can affect the market value of the collection.
Edited: Zlatko Viščević
