Coin Cleaning 101

Cleaning Techniques:

There are several cleaning techniques that I use when working on coins. There is no hard and fast rule about the proper way to clean coins, except to have some degree of patience. You can't expect 2000 years of crust to come off in one evening, although sometimes it does happen. Stubborn coins may need a brass brush. Be gentle and try not to remove "skin" of the coin. Do NOT mix cleaning chemicals or poisionous vapors may result. Read all labels, wear eye protection & rubber gloves. Be safe and smart. Take it slow or you can ruin the surface of the coin. Patience pays off on the good coins.

1. Rinse coins with soapy water and scrub them individually with a nylon brush. An old toothbrush can be trimmed down to have shorter bristles. A rubber mat in the sink helps hold the coin in place. You can also use a wooden dowl, or other object to press down firmly while scrubbing.
2. Or (more boring) Soak them in Distilled Water for several days and brush as above. The coin purists love this method, as it is the safest - but I don't really have the patience for this technique. DW is "thirsty" for dirt and crud, and cleans them very gently by leeching the mineral deposits off the surface of the coin. Change the water when it gets murky. Keep a lid on it to control evaporation. This process can take weeks, months, or longer... but will probably be the least damaging method.
3. Or (faster) Soak coins in Olive Oil for 4 days and then brush them after using a degreasing agent (TSP) or a strong dish soap like "Dawn". Repeat as necessary. You can leave them soaking for months in olive oil, and it will not really damage the coin. It may just darken them in a pleasant way.

NOTE: If you see silver or a silver-coated coin, avoid the following techniques as damage will occur. Silver is also softer than a brass brush so avoid using them. Some people report success with a mixture of lemon juice and baking soda to gently clean silver coins. Keep soaking times down to 20 minutes at a time.

4. Industrial strength cleaners/degreasers may be used as well, such as penetrating oil, WD-40, or others - but may of course damage the patina or "skin" of the coin. Blackening of the coin may also result.
5. CLR (calcium, lime, rust) or Oxi Clean might help on the really crusty ones when used for short 15 minute soaks. Kaboom bathroom cleaner can be diluted to about 30% with water and soaked overnight. Pine-Sol soaking has been used with some success. All of these chemicals will possibly change the color of the surface of the coin. If that bothers you, don't do it!
6. A brass welding rod can be sharpened and used as a "pick" to pry off chunks or blisters of crust. These can be found at your local hobby or hardware store.
7. The quickest method:
   A simple electrolysis device can be made by using an old 9 volt wall-wart power supply and hooking the negative wire to the coin (with alligator clip), and the positive wire to an old spoon. These are suspended a few inches apart in a solution of salt water (2 tablesoons per cup)... and "zapped" for 15 minute intervals. A brass brush is used in between zapping sessions, and you will be amazed at how quickly they are cleaned up! You will know it's working when the coin fizzes like alka seltzer and the crud will just come right off. The salt water will get dirty very fast. Be aware that this takes a little of the surface of the coin with it, so keep the "zap" sessions short in between brushings. Avoid creating sparks, as a small amount of flammable gas is created using this process. Try not to inhale the fumes! Chromium is released from the stainless steel spoon in the process and is not good for you. Wear rubber gloves to be safe when touching the water and such. Unplug the wall-wart when touching the coin, wires, or water. NOTE: To avoid shock, ONLY use 9 volts DC or less, and a power supply rated at 750 milliamps or less.
8. Some people claim to have had success with power tools like dremels (soft brass brushes), rock tumblers, and ultrasonic cleaning devices (less effective).