Another issue that I forgot to mention is the thickeness of the glass. Glass that is 1/16" thick transmits a much larger percentage of UV radiation than glass that is 3/8" thick. I have tested this with UV densitometer and the difference between glasss that is 1/16" thick and 3/8" thick and the difference is 1/2 to 2/3 of a stop.
Originally Posted by sanking
As far as I understand, and I have spoken to people at both Olec and NuArc about this, the glass used in the vacuum frames of their platemakers and vacuum easels is plain float glass.