1925-S-1MM-002

I use something very inexpensive to remove the unwanted crust around the letters/numbers on copper coins. You might try this on a circulated common coin first. I use mineral oil and an old worn out tooth brush. When removing the crust on the coin you might be careful not to push to hard cause the grease/oil/dark crust might contain sand and this could scratch your coins fields. So I would try soaking it first and then brush to remove the crust form around the devices of the coin. Here is one I cleaned 1/2 way. (I put tape over 1/2 so you could see the before and after.
https://www.coincommunity.com/forum...ore_Cent.jpg
https://www.coincommunity.com/forum...ALF_BATH.jpg

Never try this method on BU/proof coins as it will scratch the surfaces. But on circulated/worn coins this won't ruin the collectability as much as cleaning with an acid and remove the surface from the coin. Thus I refer to this method of removing the crud around the coin more as "bathing." Works for me but, try on a common dirty one till you get your method down before trying it on one you value. A green thorn can be used to remove some areas of the buildup. Careful when using toothpicks, they can push sand and scratch the coin.

ADDED: The green spots on copper coins will not come off or darken areas will not be removed. This is just to remove areas of unwanted crud..