The thinnest glass I can get that is acceptable for grinding is 1.94mm thick, most picture frame glass actually is not flat and has waves in it, using picture frame glass, unless the high dollar museum glass is not normally acceptable in this type of application, believe me, if it is glass, we have looked at it and tried to see how it would turn out...that is why I have the glass made for my application, but if I were to do a run of glass for one project like this, the cost factor would be hugh and not economically feasable, it sounds like the B&H route might be your best bet.