Yep, the sides and back can take quite a beating and your help to the coater in getting all the crud off of it before you send it in. A mirror sent in to a coater that needs a lot of cleaning will, of course, not get the quality of handling that something that is perfectly clean will. Of course, the front had better be superclean as you just got making that surface what it is so it better not have any crud on it. All common sense really.