What I did years back was to rub them on a scrap piece of low pile carpet, that took off what was covering them.
However if they are collectables, I would find out their value before cleaning them up, the cleaning may decrease their worth. Contact a local coin collector and see if it is ok to clean them.
Best to you.
Hello there, Leave them overnight in Coke Cola........Amazing! If it can do that to pennies, what must it do for your insides?