You do need access to the entire back of the mirror though, which is where you'll be doing all the work. (blog.jennasuedesign.com)
Some of the figures seem almost ghostly, as though poised to appear or disappear, with the tain, or lusterless backing of the mirror, revealing them as little more than apparitions. (sandlerhudson.com)
For a mind that hates external things to seek illumination in a mind where nothing exists, is to look for a reflection on the back of a mirror,» from «Reply to Mater Heng - chu's Letter,» SCP 256. (religion-online.org)