The basic supplies you will need are a stiff bristled toothbrush,
a soft brass brush, dish soap, olive oil, calgon water softener, and anything that is good for scraping (a metal strip, butter knife, steel rod, or fork prong). Be creative on finding items for scraping and poking. The list could be virtually endless. I have a thin steel ruler that has sharp edges. It is very useful for gradually reducing dirt encrustations and deposits. Possibly try a hot glue gun (pulls off dirt). I have had some success with the hot glue gun on some coins. Basically anything that you can use for soaking, brushing, scraping, and pulling dirt off with is a
possible candidate for cleaning your coins. I feel that water based soaks are best for the initial cleaning. Use olive oil for the finishing touches.
The first thing you
should do is inspect your coins. Run them under hot water and brush them with
your soapy toothbrush. Some of the coins may show some detail with a
simple brushing. You will at least get a better look at them and possibly spot a
few that have patination (a thin layer of oxidation). If you have a nice looking coin showing some
patination you will want to work on that by hand. Set aside any coins where the patination layer is mostly visible. Clean those by hand. Soak them in olive oil only to avoid removing the patination. Do not put a potentially
nice coin through a chemical soak or electrolysis.
Patination is a thin layer of oxidization
that forms on the surface of the coin over hundreds of years. Referred to as the "patina" of the coin it is most often green, brown, black, red, and blue in color. My experience is you will mostly see brown, green, and black. In my opinion red and blue is usually a bad form of oxidation. Pitting and deterioration often seem to accompany these colors of oxidation. I have also seen orange colored deposits on coins which is most often a sign of deterioration. You are generally hoping to see dirt and light surface deposits that do not break the surface of the patina of the coin. If the coin was buried with any protection it would have a better chance at patinizing before the dirt and encrustations engulfed the coin. Some coins are crystallized over time from the exposure to elements in the soil. A stress test of the coin will identify many of the worst crystallized coins by breaking them in half. Any uncleaned coin I sell has had a moderate amount of force applied to it to make sure it is not too fragile. Even the best ancient coin will break under enough force. All ancient bronze coins have varying degrees of fragility.
Now for the rest of the coins that
are really dirty even after a brush in soapy water. I recommend a soak in
calgon (water softener) and hot water. This helps loosen up the dirt and deposits. You take hot water from the faucet (don't use boiling
water) and add about 1/4 cup calgon for 2 cups of hot water. I put mine in a
small plastic clear drink bottle (separate the larger heavy coins as they may
damage the smaller coins). You then gently shake the bottle for a few minutes to
get it mixed up. You should see the water get very dirty. Let this set for
around 15 to 30 minutes and then pour the dirty water out and rinse with clean hot water. Inspect the coins and brush them with your toothbrush. If you can see much of the patination layer then clean them by hand and olive oil soaks.
Repeat the calgon, hot water, gentle shaking, and
rinsing until the water does not get dirty (or it takes a lot of effort and time
to make it very dirty). Inspect and brush the coins after each soak to make sure you don't wash away the patination. Calgon is a hard water deposit remover and will thin and eventually remove the patination layer. Only use the toothbrush at this point. Any coins that are mostly encrusted and/or showing little or no detail should be left in a calgon and water soak for around 12 hours. Rinse the calgon off of the coins with hot water. At this point you are down to the more difficult stage of hand cleaning or you can start a long olive oil soak at this point if you prefer. Remove them once a week and brush with soap and water. Either way you decide to go you will eventually have to do varying degrees of hand cleaning to finish up.
You want to remove the dirt and deposits.
Anything that is not dirt or a deposit you want to leave alone. You do not want to clean the coin down to bare metal. You want to try and keep the thin layer of patination intact. Try and force off the larger build up. Scrape
across the surface of the coin. You can also use a soft brass brush and concentrate on the thicker layers of encrustation. Concentrate on the dirt and deposits. Reduce them gradually with as little force as is necessary. Avoid scratching the layer of patination. The surface of the coin, patination, dirt and deposits are packed very tightly. Sometimes you cannot seperate them. You want to scrape and brush down to the patination layer. Do not hit metal!
Try the hot glue gun. Put hot glue on the coin and let
it dry (possibly dab it only on the dirty spots). Then peel it off. Sometimes the glue manages to pull off a bit of the deposit or dirt. It may also pull off loose silvering or patination that is over pitting too so
beware. I think it is still worth the risk though. Mainly you want to get the
coin so you can see what it is and remove most of the dirt and deposits. You should be able to remove the thick layers and even out the surface of the coin. The hot glue can possibly help remove the dirt covering the legend and details of the coin. When you have the coins cleaned to the best of your patience and ability soak them in olive oil for a week or more and brush it with soapy
water to get off any tiny bits of dirt that are left. A bright light and a small cylindrical steel rod or metal edge can be used to poke and scrape off the tiny spots that are left. A steady hand and a needle can poke out any dirt or deposits obstructing the legend or details. You are at the most risk at this point of scratching your coins.
Do not
scrub on the patination of the coin with a brass brush or any other abrasive method as you will scratch it and/or
remove some of it. Only a stiff toothbrush or other non abrasive method can be used directly on the patination layer. It is not easy to clean a coin and you will botch a
few before you get better at it. Professionals prefer to use a scalpel and a
microscope. I am going to assume for safety reasons that you will prefer to use
the methods described here. There are other opinions about cleaning coins out there. I suggest searching the internet for other ideas. Each coin may require a combination of methods to clean it properly. You should be able to finish most of your coins with the method described here.
At this stage you are going to have
a few stubborn coins that just won't clean up. This is when you have to bring in
the heavy hitter, electrolysis. Electrolysis is when you pass an electric
current through a metallic object suspended in solution. This method will remove
the dirt from any coin in a matter of minutes. Unfortunately it will also
disintegrate the patination of your coin so you should only use this method for
coins that just won't clean up. Click on my home page for instructions on
building and using electrolysis.