[78-L] Cleaning bare aluminum discs?

[Bryan Wright]

Recently at an antiques store, I picked up some 10-inch bare aluminum  
discs, including one intriguingly labeled "Paul Whiteman and His  
Orchestra" and dated June 17, 1938. The records are filthy and have  
some matter in the grooves. Can anyone offer any tips for safely  
cleaning these things? I need a method strong enough to clean the gunk  
out of the grooves, but obviously I don't want to damage the records  
(which otherwise appear to be in decent shape).

Thanks!
Bryan W.