First, mix 5 grams of sodium carbonate in 100ml of distilled water. This translates as follows: 5 grams is approximately 1 heaping teaspoonful and 100ml is about 1/2 cup of water. I suggest you use distilled/deionized water. Proceed by wrapping your crusty coin in a double layer or "pocket" of aluminum foil. One should form a cup shaped wrap to hold the solution. Add an adequate amount of solution to the cup shape and then place inside a very small plastic container of appropriate size. At this point, add the remainder of the solution.
The aluminum foil will deteriorate because the foil is acting as a sacrificial anode. The process can be continued for an indefinite period of time until the coin is clean since the the process is so mild, gentle and non-aggressive.
I have had success with this method on many coins but other coins needed to be Zapped even after the process. However, the coins may not have needed the additional Zap if I had been a bit more patient and continued the process for longer than three days.
I suggest this coin cleaning method for those who are not quite ready to Zap and are looking for an alternative method to cleaning coins. Shawn I am sure our membership(s) thank you for your contribution as I do.. God Bless.. Jerry..