If you are serious about detecting metal, you will need to know how to clean the coins you find. Today, I will write how to clean your coins that you find. There are a couple of steps, so I will get right to it.
Step 1. Pour coins, gravel, and dirty water in to a kitchen strainer over a plastic bowl to ensure that no gravel goes down the drain.
Step 2. Rinse coins with running tap water. Try not to rub it just yet because you can damage it.
Step 3. Place wire mesh basket on a large cookie sheet.
Step 4. Pour coins and gravel in the wire mesh basket, shake side to side to cause gravel to fall through.
Step 5. Set basket with coins aside.
Step 6. Scrape gravel off cookie sheet back in to tumbler to use for next time. (Gravel can be used repeatedly. Eventually it will become smooth like river rock and be ineffective at cleaning the coins.)
Step 7. Place two clean paper towels on cookie sheet and pour coins on paper towels to dry.
Before and after
Here you can here the results of using this method. First picture is before picture and second one is the after picture.