Well it turns out it is as I suspected, all you need for convincing cut glass is enough geometry in an object that has mass.
This is a room I built in Bryce real fast, mainly as a display for this door and these windows. They were at a free site, forget which but it prolly says in the readme....I'll check later; if anyone wants to dl parts like these let me know and I'll post the link. Good quality, just take a bit of adapting.
Both images use the same lighting, late afternoon/cloudy out side and sort of un-.shaded100 watt inside. Walli Hazel in the yard.