rfurman is correct but doesn't tell the whole story. When ultrasonic or wet tumbling the metal is left raw. Galvanic reaction welds the necks to the brass causing spike pressures. This is not an issue if the brass "rests" for a month or longer allowing a very fine layer of oxidation to form. Ben Stienholts (shootsdots on Accurate Shooter) Uses a nylon brush and cleans the dirty necks then uses the same brash to prep his wet tumbled brass necks with a film of carbon.