UNCLEANED ANCIENT COINS 101
You may discover many types of coins under the dirt - probably all bronze, mostly Roman, some Byzantine, maybe some Greek, and who knows, perhaps even occasionally a modern coin only a few years old. Most will be Roman, Constantine dynasty bronze. Almost all the coins will be at least 1500 years old. Most will be about the size of a dime, some larger, and some very small. Condition may range from slug to about extremely fine. The majority will be graded poor to fine. Some may be in very fine condition. Not many will be as nice as the cleaned coins in FORVM's catalog. The coins in the photo above are much better than most uncleaned coins. Coins in this condition are called "dealer cleaners." They are rarely available even to dealers.
Buying uncleaned coins is a bit like playing the nickle slots at Las Vegas. It's can be inexpensive and fun, but your odds of hitting the jackpot are slim. Uncleaned coins have passed through many hands. A silver coin or valuable rare coin may occasionally slip by, but not very often. Some eBay sellers claim ďGold Found!!Ē in their lots. Most likely these sellers added tiny foil-thin (and modern) low value gold coins to a couple lots to get feedback. We have never seen a gold coin in uncleaned coins. As a whole, when you consider your labor cleaning uncleaned coins, the coins you get will probably be worth just what you paid. But the adventure is worth much more and you might just get lucky.
The coins come from Europe and the Middle East. Before banks there was only dirt. People buried their money. If they forgot where they buried their money or died without telling someone where it was buried, it stayed in the ground. Soldiers often buried their money before battles (better the dirt get it than the enemy). Families often buried their money. Also, ancient civilizations produced coins for more than 1,000 years. People lost coins then as they do now (although they were probably much more careful than we are). Today, these ancient coins are found by people with metal detectors. About 0.25 percent of all the ancient coins minted have survived to our time.
You do not want your ancient coins to look new. Don't try to remove the patina and get to bare shiny metal. The patina, which is a green coating on most bronze coins but may be many different colors, is part of its character. Many collectors wonít buy a coin that has been stripped of its patina and a coin with an attractive patina is usually worth much more than a similar coin without a patina. You do want to clean off the dirt. Unfortunately the dirt is very often as hard as cement and very difficult to remove.
Don't give up right away on dirty coins that appear to be slugs. Often there is much more detail than you expect under the dirt! We have had a few customers write that they were disappointed because they believed that they had received a lot of slugs. Invariably they hadn't used the cleaning instructions below and were looking at the dirt and thinking that it was the surface of the coin. If you use a brass brush when cleaning small particles of brass from the brush will wear off and cover the dirt with shiny brass, this often misleads beginners to think they have removed all the dirt.
So, you don't want to remove the patina but you do want to remove all the dirt. Unfortunately as a beginner it can sometimes be difficult to see the difference between the two. If you have doubts, take a scan or picture and post it, along with your questions on the Classical Numismatics Discussion Board.
Your best friends in cleaning coins will be toothpicks, toothbrushes, soap, water, and patience. When you receive your coins, soak them in soapy water for a few hours. TSP works better than ordinary soap. TSP is a powder that you can buy in most paint and hardware stores. Mix one tablespoon of TSP with three tablespoons of warm water (increase the quantities as necessary to soak the number of coins you have). Put the mixture in a sealed container and shake well. Soak the coins in TSP solution for 5-10 minutes. Then rinse them off, dry them and see how they look. If they look nice stop. Often they need much more work.
BRONZE COINS: As a rule, bronze should be cleaned mechanically (i.e.. with brushes, and toothpicks), and silver should be cleaned chemically (i.e., with ammonia). If you are lucky enough to get a silver coin, see the instructions for silver below. Some Roman bronze coins have a thin silver plate. These coins are "silvered" coins. Silvered coins are cleaned like bronze but must be treated gently to preserve the silvering.
Use a small denture brush or soft brass bristle brush and brush them gently. FORVM sells a good brass brush made just for this purpose. If you use a brass brush alone, you will likely remove the patina and hit shiny metal on the high spots (a very bad thing to do) before you get the dirt out of the corners. Toothpicks, hardwood splinters, bamboo skewers, plastic forks and Q-tips are useful for getting the dirt from corners of the design and legend. Dental picks and scalpels will work well, but only with practice because you must be very gentle and careful not to scratch the coin. FORVM sells dental pics. Professionals usually use a scalpel but they work under a binocular microscope. Don't work too hard. Working hard cleaning coins means you are risking damage. If the coins do not come clean fairly easily stop and go to the next step. For the coins that do come clean easily and look nice, rinse them off and dry them - they are done. Most coins will not come clean with only this first step.
Soak your coins in olive oil (it is slightly acidic), WD40, or distilled water (not tap water or spring water). Few people have the patience to soak them long enough. How long - at least a few days, but weeks is usually better. Distilled water is faster, but only if the water is changed frequently (daily works well). After soaking, start over with the soap (or TSP) and water and clean with a soft brass brush and tools as described above. If they look nice stop. If they are still dirty, soak them in olive oil, WD40 or distilled water again and start over.
Other methods for cleaning bronze coins follow:
SILVER COINS: Silver coins don't have a patina but they can be toned. Toning is a thin coating usually grey or black, but sometimes with iridescent colors (rainbow toning). Just as an attractive patina can increase the value of bronze coins, attractive toning can increase the value of silver coins. Few people like uneven or sold black toning, but removing it may not improve the coin. Silver coins can be cleaned using soap (or TSP) and water, and vinegar, lemon juice, Windex, or lye. For a first soak, don't leave a coin soaking in vinegar, lemon juice, Windex, or lye unattended. Try a quick soak first. Use a Q-tip, toothbrush and towel to clean the coins. If they still are not clean, soak them again, longer this time. If they look clean, carefully wash them with soap and water to ensure all the vinegar or lemon juice is removed. To be safe, after cleaning with vinegar or lemon juice, it is best to soak the coin in distilled water with a little baking soda added for a week. (Never use vinegar or lemon juice to clean bronze coins.) Silver coins can also be cleaned by placing them in an aluminum can filled with a baking soda and water mix.
Coins should be stored in archival safe materials. Most plastic and paper will deteriorate in time and damage your coins. Even cheap coin flips contain PVC that will severely damage coins after long term storage. FORVM carries PVC free archival safe flips. These flips are about twice the price of inexpensive plastic flips that contain PVC, but they are safe for long term storage of your coins. FORVM's flips are 2" X 2" and have two pockets, one to hold your coin and the other to hold a paper insert on which you can write or type information about the coin. If you have a valuable collection you may consider buying a safe. Research this topic carefully! Many safes keep documents safe during a fire by sealing in moisture. Moisture can cause bronze disease, and often other things that could destroy your coins.
Renaissance Wax is a special conservation wax, sometimes used to coat coins and protect them from the environment. Most collectors do not use it and it is not necessary. If you use it, follow the instructions on the label. Renaissance Wax may be a good idea if you live in a very humid environment and your coins are exposed to humid air. Renaissance Wax may be used to preserve coins that have been treated for Bronze Disease (see our NumisWiki article on Bronze Disease for more information).
Now that you have cleaned your coins, you will want to find out what they are. FORVM has many online resources to help. Use our romancoin.info. First, remember that the bulk of your uncleaned coins will be late Roman, that is to say, Constantine I and later. Look through our catalog for the same type. Use wildwinds.com, a large online database for ancient coins. Ask for help on our discussion board. By the Handbook of Roman Imperial Coins or one of our other book offerings.