I'm giving in to glass transparency right now, (weird, because I tend to sneer at artists who substitute transparent bling for a voice). What's utterly fascinating is the almost symbiotic relationship that transparent sculpture has with its environment. I want to learn to use that power in my work, and from what I've seen so far, it'll be a helluva challenge.
Sculpting with glass is, for me, an extreme exercise in controlling the viewer's eye. The artist directs the viewer's eye with all art, of course, but in other media that control is largely confined to the surface. A work's mass and volume are simply vehicles for presenting (or hiding) whatever the artist has put on the surface.
Not so with glass--you can send the eye anywhere you want in that volume; surface constraints only exist if you choose to use them, i.e., opaque the glass.