This is how glass is hand-cut! Following all my stained glass posts there was some confusion as to why certain shapes had to be separated into two pieces of glass and how do you even cut a piece of glass to the shape desired. So here are some photos and explanations, hope this helps!
Tools you need:
Cutter (green), snappers (black), special pliers (blue), glue stick!
First of all, the pattern you have chosen needs to be labeled and cut out with special three-bladed scissors:
Then, pick a piece and glue it onto the glass. The cut will always have to go from one edge of the glass to the other (can’t stop a crack in the middle of the glass sheet!) so a bit of strategy is required as to not waste too much material. Pick an edge to cut first (again, strategize: cut the side that is closest to the edge first, that way if the cut fails you can always just shimmy up the paper a bit and re-cut). The cutter is basically a small serrated wheel (like a pizza cutter) that introduces flaws to the glass along a line. On the photo below you can see the white line created by the cutter:
Then, you can either use the snappers is the cut is more or less straight or the pliers if the cut is too curved. Or a combination of both (use snappers to prime the crack at the edges and use pliers to finish propagating the crack), or just how you feel like it - it’s kind of a skill to acquire.
So now it becomes apparent that certain shapes cannot be cut this way - inward angles for example and inward curves that are too steep. If you have a rather small radius of curvature you can iteratively cut into the curve (see below) to release the friction “pressure” of the sides (it’s… difficult to explain…)
Welp, that’s it for cutting. The edges are kind of messy at this point so next step is grinding!