Many spray paint products have been tried-—silver, chrome. nickle-—but Krylon Looking Glass does the trick. Hard to find-—but Hobby Lobby has it.
Some crafters spray droplets of water inside the glass before spray painting——has that antique look after it dries.
I’ve done painting like that; spraying droplets of water, before spraying the paint. I usually did a base coat of one color, then did the spritzing thing with a contrast, usually gold or silver, because I did the items for a Christmas fair.