Ye Gods, its so simple, providing the glass to be cleaned doesn't have a plastic film or coating of some kind on its surface then simply use soapy water either from a hand sprayer or your applicator and use a razor scraper such as all of the major window cleaning equipment manufacturers produce and be it tape paint or a myriad other things that can get on the glass and they are removed with absolute ease for the most part.
But beware of....whats the proper term?....manufacturing debris?....anywho, test a small section of the class if it is hardened or tempered/toughened glass as if it has this debris on it don't go anywhere near the glass with a scraper.....or you will be sorrryyy!!
With plastic films on the glass surface just give the owner/manager/customer a bit of a bollocking because then it can be a major hassle to get tape residue off, be careful with solvents in case the film also gets dissolved....not that meths or white spirit will affect the film or coating at all but some of the stronger solvents may well do so so care ius needed.
fabrication debris!!! thats the word I think I was looking for!!
Ian
