There are many methods people use for cleaning ancient coins. Likely if you are reading this, you are looking for some good guidance. Probably the easiest thing to do to get yourself started is to soak your coins in olive oil. Many of the better coins in a lot will clean up quite easily and be attributable with just a few minutes in some olive oil and a gentle brushing with a nylon brush. It is a good idea to purchase a low grade lot to get used to cleaning coins using methods beyond this.

When purchasing coins, be very cautious of those who promise gold and silver. You will never clean an encrusted gold coin. Dirt does not adhere well to gold coins, so they are easily distinguishable as soon as they are dug. The likelihood of anybody selling one in an uncleaned lot is about as low as the likelihood of being struck by lightning. You will occasionally get silver coins in larger lots, low quantity silvered coins are more common.

You now have you low grade lot and are ready to get busy, pull out those ones that are obviously pretty much slugs, work on them first, you have nothing to lose. Try all types of things and pick what you like. If you like toys, ultrasonic cleaners are a cool toy that takes much of the work out of coin cleaning. Heavily encrusted coins may take many cycles to clean, but you will likely do less damage to the coin using these.

Another popular method is electrolysis. Many sellers offer kits on ebay, I recommend if you have any tinkering skills at all to build your own, it is very easy to do. Go to an electronics store and by a wall plug transformer that converts 120 V AC to 9 or 12 V DC current. Cur the jack off the end and separate the two wires so that you can work with them separately. Attach alligator clips onto the wires. Take an old margarine dish or something like it and fill it with very salty water. Attach one clip to a nail or something like it, the other clip hook to the coin, dip both in the water. If the nail bubbles you are connected backwards, simply reverse teh connections and go to town.

For soaking and brushing you may choose to use something more aggressive than olive oil, some people like WD-40, I have had good results with that. Others who are very patient like to use distilled water and simply allow them to soak for months on end. Whatever method you choose, remember that a bronze coin is more valuable if the patina is not affected, what ever cleaning method you choose should not remove the patina. This is why you practice with some low grade slugs first, this way you will not be disappointed when mistakes are made. Once you have selected and perfected you method, purchase some better coins and have fun.