Bob - wish I knew what that Zeiss glass I bought a ctn of long ago was originally meant for. It's got
a smooth coating which is highly abrasion resistant and somewhat suppresses rings, but it's not a
typical optical coating. About 2mm and fairly tough (took me 20 yrs to finally break a piece). In cutting behaves like tempered glass. Very flat optically. Odd size, metric, but almost 12x16. The Zeiss part number hasn't led me anywhere so far. Maybe not suitable for high UV transmission, but
works perfectly for ordinary VC blue filter split printing.