Chiseling. Gotta love the chisels.
Plus, doesn't he have great hands? Beautiful.
There's something amazing and deeply satisfying in the way glass pops apart when you give it a good clean cut. If you've never cut glass before, I'd say go cut some glass. It's nice. It's very nice. And this is all you need to do it: glass cutter, straight edge, glass.
Simple, easy, and awesome.