Hometalk has a whole bunch of relevant projects: https://www.hometalk.com/search/posts?filter=mercury%20ornament.
Check them out and see which speaks to you!
Hi! Here is a post on that for you!
I think this is what you're looking for:
All you need for this is some of the mirrored glass paint and a spray bottle of water. Spray the ornaments then immediately spray them with water. It works really well and looks great. I used this technique on some glass bottles/vases. https://michellejdesigns.com/diy-mercury-glass/ Have fun.