I’m considering getting 2 yellow gold lunaria pieces. I’ve noticed both in pictures online and some older pieces in store that his pieces can get black marks on them. Has anyone had this happen? And if so, will it come off with a good cleaning? These pieces are expensive and I don’t want to invest in them if they’re going to turn black over time. I’ve never had a gold piece do that so I’m wondering what causes the black marks on his pieces? I’d love to hear from folks who have had these pieces for a while and whether they’ve had any issues with these pieces essentially tarnishing (or whatever the black coloring is). Thanks!