IOR
Holy index-of-refraction, Batman!
I agree with a previous review that the glass is awesome. The background pieces particularly look realistic. In the foreground pieces, the rook most of all, the distorted image within the glass is really sharp: too sharp to be realistic, but not to sharp to be stylish! It's a great image, and even the way in which it is "flawed" as a representation of reality, it still looks awesome.