To paraphrase the most famous line from Shakespeares Hamlet, with regard to coin finds, the treasure hunter must ask, To clean or not to clean, that is the question.
It is a difficult question. Purists maintain that one should never clean coins. Most, if not all, cleaning methods can damage a coins surface, rendering minute details unreadable or obliterating them altogether. A cleaning can also destroy the green color highly valued by many collectors, called patina. Indeed, a fine patina lends a certain romantic look to the coin, a certain antiqueness that is so desirable some interior decorators purposely age furniture to create the distressed look.
For collectors, cleaned is the numismatic four letter word a profanity so insulting that a mere mention of it creates a stigma attached to the coin, and often the seller, that sends a potential buyer walking away never to return. A good clean, and this phrase may be in fact an oxymoron (no clean being a good clean), can devalue a coin or render it worthless.
Sometimes, along with the dirt and the patina also goes some of the surface metal, and goodbye to subtle detail on the coins surface (see photograph of a bad clean done in Coca Cola).
If dealing with a rarity caked with the earth from which it came, consult an expert numismatist and leave the cupboard holding commercial solvents closed!
With that established, sometimes a coins surface remains unreadable without some amount of cleaning, and those interested in fun who arent concerned with rarity or resale value may want to give their finds a little bath. The following tips provide some insight into the taboo subject of coin cleaning.
The basic idea is the less damaging, the better. The softer the metal, the more potential to cause damage when cleaning. No matter who a person consults, one common denominator exists with regards to cleaning coins: begin with soaking the coin in distilled water and, after a lengthy soak to loosen the dirt, work it away with a soft-bristled instrument like an old toothbrush. If distilled water doesnt do the trick, a quick wash with soap may loosen the dirt clinging to the coin that can then be harmlessly brushed away with the toothbrush. If dirt still remains, a blunt edged, yet relatively soft object can be used to pick away the dirt clinging to a coins surface. Some coins that have reposed in dark sediment such as mud for years may come out of the earth black or covered with black blotches. This skin cancer can be removed with a toothpick or even a plastic knife or fork. If possible, avoid metal objects with sharp edges such as a hairpin, paper clip, or Exacto knife, as these can leave the coin scarred with scratches.
A toothpick allows a person to chisel away at the dirt caked around the coins finer features, such as letters or numbers, without obliterating them.
If, after hours of painstaking chiseling, the dirt remains, its time for stronger stuff. Toothpaste is one of the most underrated cleaners on the market today, as anyone with young children can testify. Squeeze a little toothpaste onto your fingers and massage the coin between them, then rinse with water. You may need more than one application, but this method may remove much of the dirt clinging to your coins and, when combined with the toothpick, leave the surface of the coin legible yet relatively undamaged.
Relatively is the proper word, because this mild abrasive can damage the coins surface. A few applications left the raised shield on a Civil War token with an unnatural pink tone and a scuffed appearance (see photograph).
The Dirty Discs Can Be Transformed Into Collectible Relics
Another less damaging way to clean dirt from coins involves olive oil. Soaking coins in olive oil for a few hours, or days or weeks (depending on the amount of dirt on the coins surface) can loosen the sediment that can then be removed with an old toothbrush. Lemon juice, a mild acid (as far as acids go), can also give a dirty coin a good bath.
More exotic methods do exist. Many treasure hunters prefer to employ electrolysis, but any method that involves a DC battery and water requires further research. Only pursue this method if you have done your homework (several websites provide instructions for using electrolysis). Electricity, water and humans do not mix.
A number of methods exist involving baths in various chemicals and industrial-strength solvents. Some use tri-sodium phosphate (TSP), but TSP can be dangerous. Others recommend soaking coins in Coca-Cola for a number of hours, but this rather acidic compound can also damage the coins (and you wonder why people who drink soda often visit the dentist!).
One treasure hunter known by the author even used a rock tumbler, which produced lovely circular bits of shiny very shiny metal, but essentially obliterated the delicate features on the coins. Another used Brasso, which left him with wonderfully shiny and attractivebut worthless coins. His kids loved them, though.
With the help of a little soap, toothpaste, olive oil, and tenacity, the dirty discs that surface when you coin shoot can be transformed into little collectible relics.
A "bad" clean The damage that can be done by excessive cleaning is evident on this Civil War Token. The cleaning destroyed many of the details on the surface of the coin.
The other side of the same coin is shown which has been cleaned with a few applications of water and toothpaste.
A little toothpaste will go a long way. This Civil War token was found embedded in mud with a metal detector. The coin emerged from the earth a jet-black color, which can be seen around the stars. With a gentle rub of toothpaste, the details of the coin became visible, although the toothpaste did leave some abrasion on the shield.
The Good Clean: The same type of Civil War Token is shown as a comparison to the cleaned one, illustrating the potential damage excessive cleaning can do.