Pickle for brass and brass with silver added


I have a few customers who are casting brass and or master alloy
(without the gold in it) and making jewelry.

It seems to be difficult t pickle cast brass and then go for a
magnetic tumbling. The castings are turning white, like a steel
coating, from magnetic pin tumbling.

We hope to find a pickle alternative for brass, rather than a long
multi step tumbling process. The items can NOT be hand finished.

Any help sure would be appreciated.
Daniel Ballard