Sorry, David... i was referring to the glasses used in picture framing. I'm sure there is alot of stuff out there that we would be amazed to know about.
But I was speaking of framing glass: If you look at framing glass edge-on and it appears green, it's likely less brittle than glass that appears white (the "water white" framing glasses or orange (as with museum glass). In addition, the micro etching that gives museum glass its invisible surface (as with the now-defunct Denglas) makes the glass more brittle.
