Learn about this topic in these articles:
Because electrons in glass molecules are confined to particular energy levels, they cannot absorb and reemit photons (the basic units of light energy) by skipping from one energy band to another and back again. As a consequence, light energy travels through glass instead of being absorbed and reflected, so that glass is transparent. Furthermore, the molecular units in glass are so small in...
Opacity is one of the most desired properties of printing and writing papers. Satisfactory performance of such papers requires that there be little or no “show-through” of images from one side of the sheet to the other. Satisfactory opacity in printing papers requires that white mineral pigments be incorporated with the paper stock or applied as a coating.