The large mirror in my hallway of mirrors came from a charity shop for a few quid. It was garish gold with a hideous cardboard picture of a cottage stapled into the back. I pulled that out and gave the plastic frame a good scrub in the bath.
I stippled on a dark grey chalk paint then rubbed over it with a candle followed by two paler colours in emulsion with less coverage.
Then I stippled on some dark wax, pushing it into all the nooks and crannies, let it dry and buffed if off.