How do I properly verbs nickel silver? I made a necklace in a metalworking class out of remaining scraps...

I made a necklace in a metalworking class out of remaining scraps of nickel silver. I completely forgot it wasn't sterling silver similar to the rest of the jewelry I made in that class and cleaned it beside sterling silver cleaner. Now it's a blotchy brassy brown color. What are the proper cleaning materials for nickel silver?
Ok I get one for you?
Answers:    Buy AUTO SOL Silver and Gold cleaner from known hardware/ stores. It's cheap but immensely effective.