I am in the metal detecting hobby and clean my modern pennies in a rock tumbler with lime away (so I can cash them in/spend them). It shines them up like crazy. The pennies have to be rid of dirt & other stuff though. I use liquid soap and water & tumble them in aquarium gravel to get the dirt off..... then rinse off the gravel & tumble them with lime away. Might be worth a try.
edit: I once saw an old large brass silver burnisher that operated the same as a rock tumbler. If you ever found one of those while out scrapping I bet you could use it to tumble-clean copper if it is cut into small enough pieces (like say... about a foot).
Edit again... I just found a pic of what i am talking about... can be seen here...
http://www.worthpoint.com/worthopedi...bler-polishing
Edit: again... found some pics of a similar one... gives you an idea of how it operates better than the other pic.
http://www.practicalmachinist.com/vb...achine-239535/
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