I do not know what the shape and size of your material is, however, you might like to , generally, look into the subject of rock tumblers.
Rock tumblers (particularly the vibratory types that don't technically 'tumble' the material) can be used for many purposes, depending on how and with what they are filled. One such application is polishing brass pistol and rifle cartridges. These are popular with people who reload their own ammunition. There is a ton of info on the net on this topic... (I have been away from it for a bit, so my references likely lead to a bunch of dead ends) .. just fire up your favorite search engine and search for _rock tumbler_ and maybe add things like metal polishing, abrasives, polishing agents, etc as additional search terms.
Also, there are some fairly pricey hobbyist and semi-pro rock tumblers for sale on the net, but I recall that Harbor Freight has several models and sizes that are very reasonably priced and are 'rough and ready' but you will have to supply your own abrasives/materials/shot/polishes. Check it out.
Good luck,
diogenesNY