How do they get the hole going through the pipe (making it hollow)	back

These are often the thoughts of someone being exposed to 'hand blown' glass pipes for the first time. For starters, the raw glass is available in both rods and tubes of varying sizes. Pieces of this tubing are rotated in the flame of a torch, and heated until the glass is pliable (think of a sugar-daddy on a hot day, or honey at about room temp). Once the glass is in this semi-liquid state, it can be manipulated with various tools, gravity, and by blowing into the hot tube. Patterns are added by applying colored rod, and/or encasing fumed on metals (mostly gold and silver) with layers of clear glass. I realize this description raises many more questions than it answers, but the process is really too involved for me to go into more detail here.