How to keep copper jewelry shiny

I recently got a copper necklace wire wrapped amethyst pendant. So beautiful and only had a few days. It’s suppose to have a tarnish resistance finish. I noticed it’s looking visibly darker and it hasn’t touched water or anything. Will copper not stay shiny like that? How can I clean it without harming my amethyst stone? I wanted it to be a daily wear piece and also wear to my wedding.