for all the coins, copper-silver-brass I use the following methods
1-in a glass
of warm water, put 1 or 2 sodomite for 15 minutes and put the coins.
2-with dremel I clean the coin. wire brush and post plastic brush gently.
3-if needed I clean the corners with the pencil
4-difficult coins with iron rust make electrolysis
12v. in water and soda water pot