Planet Spanning Hole?

[starslayer]

Glass is not a fluid, it is an amorphous solid. It does not flow; older stained glass windows were made from roundels of crown glass which were thicker at the edges due to the manufacturing process (they were formed by spinning glass around the glassblower's pipe). Panes of glass were cut from the roundel, and the thicker parts were simply oriented downward for stability. More recently, flat glass panes were produced by pouring molten glass over a polished metal surface, which still produced a thicker side near the location of the pour. Modern panes are produced by floating molten glass on a liquid metal surface, which produces a very uniform, flat surface on both sides of the glass.

Thanks for correcting me on the liquid/fluid part; IIRC, the only truly liquid part of the Earth's interior is the outer core.