How to make Prince Rupert's drops - glass that fractures at the speed of high explosives

NightHawkInFlight doesn't specify which type of glass he's using, but I'm pretty sure it's just soda lime glass (available from Flinn Scientific, at least that's our common source for the summer camps.)

The technique for making Prince Rupert's drops takes a little practice but really isn't all that tough to manage with a little trial and error.

Here's another POV - including a fair bit of the science and where Prince Rupert's drops would fit into a science curriculum.