Cleaning Ancient Coins
By Josh Moran, WINS#62
Cleaned. A word that most coin collectors hate to hear. This is certainly understandable for collectors of modern United States and World Coins. For collectors of ancient coins, however, the word is not as abrasive to the ears. The fact of the matter is, nearly all ancient coins have been cleaned at one time or another. In order to maximize both the value and enjoyment of these coins, they are cleaned.
Most ancient coins are brought to the market by metal detectorists in Europe. These coins have spent as much as 2700 years in the ground. That's plenty of time for dirt, sand and organic matter to adhere to the surfaces of these coins. Additionally, corrosion may have formed due to moisture or soil acidity, further complicating the problem. The build-up of dirt and corrosion is usually enough to make a coin unattributable, thereby hurting its market value. In order to maximize both the value and enjoyment of these coins.
When it comes to cleaning, some methods are better than others. The most common of which is the "soak and brush" method. Coins can be soaked in a variety of liquids to loosen the dirt encrustations. Olive oil, lanolin oil and distilled water are among the most common of these liquids. Brushing these coins regularly between soakings with a stiff bristled brush can help to remove the majority of loose dirt and other encrustations from these coins. Toothpicks, rose thorns and cactus spines can be used to flake dirt out of fine details such as hair, eyes, and letters. Dental and brass probes can be used also, but care must be taken not to scratch or otherwise damage the underlying metal. This process generally takes a long time and can be used on coins of any metal composition. It generally produces the most attractive coins though.
For coins of a predominantly silver composition, exposing the corroded/dirty surfaces to citric acid can be an effective cleaning method. This process involves placing a coin in a citric acid solution (lemon juice for example) and then wrapping it in aluminum foil. The resulting chemical reaction helps to remove corrosive buildup on the surfaces of the coin. Caution must be used in this method with coins of high copper to silver ratio, as the citric acid can further damage the coin. Additionally, this method can produce strange toning/patina on the coins surfaces. The results of this method are generally a crap-shoot, with some coins coming out spectacularly, and others so-so.
If the "soak and brush" method does not work, a more harsh form of cleaning can be used, known as electrolysis. This involves immersing the coin (or coins) into an electrolytic solution (usually saltwater) and passing an electric current though it. The resulting chemical reaction causes most debris attached to the surface of the coin to come loose. This also includes any original patina present on the coin. This process must be used carefully and sparingly, as it can completely destroy any coin that is subjected to it. Museums often use this method for metal objects that they clean for presentation, as their main concern is the preservation of the item, and not necessarily the collector value. Even if the patina of a coin is stripped when using this method, a number of products are sold nowadays that can be used to repatinate coins. Cleaning coins using the electrolysis method is usually more likely to produce coins with unattractive eye-appeal. The process is, however, the fastest of the three discussed here. This is only a sampling of the most common cleaning methods used on ancient coins. Professionals and collectors alike are always experimenting with new methods.Some work well, others don't. Part of the problem in finding a good universal cleaning method is that each coin has weathered the elements differently. Depending on its original composition, where it was found, how long it was in the ground and how soon conservation/cleaning begins on the coin all affect which method will produce the best results.
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