Cleaning Ancient Coins
The first step in cleaning ancient coins is to acquire some. Ancient coins are those older than medieval times and some of the most plentiful are from the Byzantine Empire. Uncleaned coins can be purchased singly or in lots of ten to a thousand or more. For your first venture into this form of treasure hunting, it would be wise to start small with twenty to fifty coins. Expect to pay about 50p upwards each for these bits of antiquity. Also expect them to be mostly small and made of bronze. Most uncleaned coins offered for sale will have been gone over with a metal detector to winnow-out the gold and silver ones. Don’t let this deter you, however, as a lot of the fun of this hobby is scraping off centuries of dirt and corrosion to catch a glimpse of a laureate profile or Latin inscription.
When your coins arrive, they will be more or less disc-shaped and many sound metallic when giggled. They will be covered with dirt or worse. Your task will be to clean them enough to see if you have attributable coins or worn slugs of ancient metal. If you are already familiar with collections of modern coins be prepared to lower your standards considerably. Perfect, uncirculated ancient coins are very rare and unlikely to turn up in odd lots of uncleaned coins. The standards applied to ancient coins make allowances for the centuries they have been in existence, squirreled away in usually damp and dirty hiding places.
Any coin that still shows traces of its original stamped image will probably grade poor to fair. Coins that have recognisable images and inscriptions will be good to very good to fine or very fine. Do not be discouraged if you find coins that have images that are off-centre, contain holes, or show signs of having pieces sawn off. Remember that ancient coins were hand-made using blank discs of metal and special mint dies. A blank was placed on the bottom of the die, covered with the top die and stuck sharply with a hand-held mallet. Less skilful workers would produce sloppy coins. Large denomination coins were sometimes cut into smaller pieces to make change and coinage was often altered by succeeding regimes by piercing or re-striking. It was not uncommon for ancient people to make a small cut in a coin to make sure it was solid and not just plated with precious metal. There are collectors that specialize in altered coins. Don’t throw anything away just because it looks less than perfect.
Before you start cleaning your coins you will want to assemble a few tools and some chemicals.
Tools: A good source of light is essential. Craft shops sell magnifying lights that are very useful, especially if you do not have a stereo-microscope. Empty baby jars are very handy for holding liquids and soaking coins. You will need an old toothbrush for scrubbing the coins, toothpicks or dried rose thorns for picking out bits of dirt, and cotton swabs for working on small areas of a coin. Remember that ancient coins are fairly soft metal, bronze, copper, silver, or gold. You do not want to scratch the surface of the coin while cleaning it nor do you want to remove any patina that may have built up over the centuries. Your object is NOT to reduce your coins to shiny like-new condition.
Chemicals: Most of the dirt on your coins will yield to soaks in distilled water or olive oil. Avoid tap water, the chemicals in tap water can harm your coins and destroy any traces of patina that may remain. More encrusted coins will clean up after soaking in olive oil. Use the least expensive oil, not extra virgin. Very persistent dirt can be removed with WD40 or a combination of baking soda and vinegar. These last two should be used only as a last resort as they can change the colour of the patina. Vinegar and baking soda can also worsen pitting on already pitted coin surfaces.
THE CLEANING PROCESS
Sort your coins before you start cleaning them. If you are very fortunate, you will have some that will need very little cleaning to be recognizable. Keep these coins in a separate jar as they will not need much work. If you only have a few coins, put them in a small dish or baby food jar and cover with distilled water. Allow them to soak for an hour or so then pull one out and rub it with you fingers to see if the dirt is softened enough to remove. If your fingers get soiled, use the toothbrush to scrub away at the surface.
Do this with all the coins, one at a time, rinsing each one in more distilled water and drying carefully with paper towels. Examine each coin under magnification, either a hand lens, magnifying light, or stereo-microscope. Some of your coins might be pretty clean just from the water soak. If they are still encrusted with dirt, a longer soaking, over night or for several days, in fresh distilled water might do the trick. Repeat the soaking, scrubbing, rinsing, and drying a second time. Coins that are still encrusted wit dirt and corrosion should now be put in olive oil. Use a container that has a tightly fitting lid so that you don’t spill the oil accidentally. Dirty olive oil is very messy to clean up. Let your coins soak in the oil for a day or more. You can pull them out, brush them with the toothbrush and blot with paper towels, and examine them under magnification. As the dirt comes off, remove the clean coins from the oil but return the still dirty ones for more soaking.
As the dirt and corrosion comes off the coins you should be able to see images and inscriptions. If, as you work you way through the cleaning process, you cant see anything you may have to accept that you have a worn-out slug, a coin that has been through many hands and all the images are rubbed smooth. Fifty years of constant circulation is enough to remove a most vestiges of relief from a coin.
Patina is not present on all coins. It is a coating that develops on metal after many years of use. It can be greenish, brownish, or greyish in colour and many collectors consider it one of the beauties of ancient coins. A coin with excellent patina can be forgiven a slightly worn image. For instance NEVER do anything to a coin that will remove the patina or change its original colour.
Coins that show good images, patina, and some inscription are worth a more careful examination under magnification. Here is where you will want to start picking with a toothpick or dead rose thorn. Work carefully under magnification and try to dislodge bits of corrosion from between letters and around details. If you have a hot glue gun, plug it in and drop a glob of glue on the coin. When it hardens, lift the glue off and a lot of dirt will go with it.
METHODS TO AVOID
Do not be tempted to use metal brushes, rock tumblers, ultrasonic cleaner. All of these methods will result in smooth, shiny, metal slugs, NOT attributable coins. Also avoid the use of harsh chemicals. Experts make use of formic acid, sulphuric acid, and silver nitrate but in the hands of a beginner these chemicals can ruin coins and cause injury.
IDENTIFYING YOUR COINS
If you are very fortunate and discover a coin in very good or find condition you will want to identify it if at all possible. There are many books available to help in the attribution process or you can take your treasure to an antiquarian for assessment. Some will do this for free others will expect a fee and some might even be interested in buying your find. Coins of little or no value to a serious collector are still interesting and can be used to make intriguing pieces of jewellery. Craft shops sell bezels for enclosing coins to make pendents, broaches, or charms. Coins can also be mounted and framed for display.
Finding a valuable coin or not, the enjoyment of handling real money that ancient people used in their daily commerce is a big part of cleaning coins. You may develop a deeper interest in the history of Rome and Ancient Greece and collecting the coinage of those ancient civilizations is like travelling back in time.