I have some nickel brass that I got from someone else. I am pretty sure that he cleaned in an ultrasonic cleaner because it is black, and that is all he has to clean brass with.. I have tried tumbling it with stainless steel pins. The stainless takes off some of the black but it takes tumbling it 4 or 5 times before it starts any noticeable effect. Does anyone know of another way to get the black off and the nickel back to silver?