How can I tell if a mirror has mercury in it?

Mercury mirrors were made with a thicker glass layer than modern mirrors, so one way of identifying a mercury mirror is to test the thickness. Take an object like a pen or toothpick and press it against the mirror. If the object looks like it’s touching its own reflection, then the mirror is thin and not a mercury mirror. However, if the object appears separate from its reflection, the thickness indicates that it’s probably a mercury mirror. Shop a collection of antique mercury mirrors from some of the world’s top sellers on 1stDibs.