DO NOT CLEAN.
The only cleaning, only when they are realy dirty, is warm water, soap and your fingers.
Everything more than this will decreese the coin value.
Citeer: EmJay05I've heard of using an easer - is that bad ?
YES IT IS BAD.
The coins should have a nice patine according to its age.
This patine only increeses the value of the coins.
They should not be cleaned as if they were a jewels.