You can clean in a tumbler or a vibratory, but some pre set up work is needed. a piece of flat stock 5/16" x 1"x the length of the blocks. 2 zip ties. ( or drill the flat stock for the mount screws) the flat stock will space the blocks apart so all surfaces get cleaned but the handle cuts. Drilling and using the screws works better and gives better cleaning. Attach one block to each side of the flat stock this locks them together so faces can bang into each other. Load the tumbler with fresh corn cobs and fairly full when running check often. I have done this on badly corroded moulds and gotten good results. for light rust and tarnish a brass or nylon brush and solvent does it. For rust in cavities I prefer to cast some slugs and lapp the cavity with flitz simichrome or tooth paste. A good soaking in kroil is a good start.