yes-forgot what it is called,but often forms on older coins.It does clean off andthere is a product made to remove it without harming the coin. There is a thought that one should NEVER clean a coin,with anything,as it loses value if you do,so I leave them as they are. I'm ssure this coin would clean up nicely,but I leave that to the buyer's choice. Thanks for looking--(now I know my pictures are,at least,useable!! lol)