I'm looking into sculpture involving suspending objects within negative space. I've seen sculptures, tabletops and other objects which use clear plastic, from a resin or something. Googling yields many, many different plastics which could achieve this, but may not be ideal. What are some of the processes and materials generally used by artists for this kind of effect?

I'm looking for a glass-like (hard, dense) effect right now, but really I'm just looking for an intro to sculpting with, and inside clear materials.