Do you see how the ice-cube is less transparent in the center in this image? http://p.lefux.com/61/20091013/A10470000C/Crystal-LED-Ice-Cube-1-Gallay.jpg [Broken] This image doesn't capture exactly what I see in my cup but it gets my point across. Why is an ice cube less transparent in the center? I'm guess it's because the atoms are more tight bonded in the center. But if that's true then 1. why does that make them less transparent? 2. why are they more tightly bonded in the first place? I put this question in general physics because it doesn't seem to deal with any one area of physics except maybe classical physics.