This stunning crackle effect is created by painting slip (with added sodium silicate) on the outside of a newly-thrown narrow cylindrical pot. This is gently dried with a blowtorch so that the outer layer cracks as the pot is stretched into a pleasing rounded shape. This is a particularly challenging technique, as the potter can't touch the outside of the pot as it is stretched, because that would eliminate the texture. There is also no opportunity to trim and refine the pot once thrown, which means the walls of these pots tend to be thicker than traditionally thrown and trimmed pots, making them a little heavier and more substantial.
 
In this case, the stretching process has been pushed past its obvious limit, leading to interesting cracks right through the clay. Of course, this means the pot cannot be used to hold water, or at least only up to the bottom hole!