polish it with metal polish(brasso will work)& buffer like for your car(you can get 1 to fit a 7" or9" grinder).then use a cover lens or plexiglass.

I've used old car/truck mirrors, used to carry an extra one in my rig.  Nice thing about it is it gives a large view of the weld- something you don't generally get from the manufactured ones available which usually are only 2' X 4".  I liked the having the bigger view of things for perspective, and a wrecking yard vehicle mirror shouldn't cost more than 5-10 bucks.  Tape a couple of clear lenses over it as someone pointed out and position it as far away from the weld as you can and still get the view you need......Mirror welding.......jeez.....they better be paying an extra couple of bucks for that at a minimum.