Low e coatings have been used on the fourth and first surface of IG Units. So these metal alloy thin films are vulnerable to chems and abrasives. They are VERY easy to scratch. What is fascinating to me is that it is possible to remove such scratches with the right superabrasives. I have done it and have talked to guys that have also. Of all of the tech stuff I have looked at over the last thirty years abrasive tech has always been the most interesting.