I am not exactly sure...I believe its just a base metal and then they coat it with a different metal if that makes sense...sorry if that's not any help :( I don't have the books anymore to look it up.
I used to sell Premier and I still have a catalog. It says it's antiqued matte silver plated. I have this set and I love it. I do know that almost all their jewelry is either silver, gold, brass, hermitite or rhodium plated. It's great high end costume jewelry. Hope that helps.