I have a full wall vanity mirror (70" x 42") in my bathroom wall. I need to drill some holes through it in order to install a vanity light. I realized that if the mirror is made from tempered glass it might shatter completely if I try to drill on it. The mirror probably is construction grade installed originally when the house was built in 1988.
Is there any way to tell if a mirror is made from tempered glass or not, without breaking it, and assuming that there are no "tempered glass" labels anywhere?