Dear Cecil,
I am flabbergasted at your answer to Daniel on the clarity of glass. The transparency of glass has absolutely nothing to do with it being viscous/crystalline/solid/liquid. It has only to do with the electronic properties (note water is opaque to light of wavelengths below 290 nanometers and between 30 micrometers and 1 cm). Also, the density of the
substance again only matters in so much as the closeness of other atoms/molecules affects the electronic structure.
If your primary argument were true, liquid metals should be transparent and quatrz and diamond should be opaque! While you recover more of the correct reasons in the last paragraph, what you use as your basic argument is unfortunately complete nonsense.
Paul Voytas