I’ve found that if you ignore the directions and DON’T clean the glass, or even deliberately dirty it, and then build up the coating in several light and very uneven coats, you can passably mimic the way antique mirrors darken and wear unevenly. You can even add a spritz or two of dark grey paint between coats to mimic those antique mercury spots. It’s fun to experiment, and if you hate it, you can scrape it off. Once you have it the way you want it, there’s a sealer coat that makes it more durable. I hung mine outdoors, and they lasted through four Maine winters before a really big windstorm tore them off – but the shards still looked pretty!