Using "Mothers Mag &Aluminun" polish on nickel and wondering when is it time to stop, each time i apply a dab. i still get "black" crud, wipe it off, apply more and same crud! Question is, is there a time to stop or just keep applying more Mothers and wiping, will it eventually rub through the nickel or finally leave u with like perfect finish? ( Gun is a 2006 Beretta 85) thanks