I usually tumble the worst of my clad. I use water, a touch of Dawn, and some aquarium gravel.
For anything of value I tumble with walnut shell and corncob. The walnut shell is more abrasive than the corncob. Often the corncob has some wax or polish in it, and its softer and less abrasive. Both medias are softer than coins/metal so it can't hardly hurt them. You can get the media where they sell reloading supplies.
I have dug a few AU barbers, and after a couple hours in the tumbler they look mint