How to cut a glass tabletop - GIF

[CharlesWaugh]

They have to go that fast because they have already done the vertical scores on the glass (note that the guy in black breaks it over the edge of the table then also cross-wise in his hands before putting the two pieces in the stack).

Speed is important, because the cracks that the scoring tool makes quickly begin to heal and then the break gets ragged or even runs off-score, making a terrible mess.

At least, that's what some 'old boy' window glass guy told me - it makes sense. I also seem to remember some Scientific American article about crack porpagation and self-healing of glass, but I can;t find it with a quick search.