Stu and Alex likely already know about this stuff, but I thought this was interesting. Hikaru dorodongo are spheres of mud hand-made in a painstaking process, polished to a high gloss.
One comment on this website made me think of woodturning. There are some similarities...
As an aside, this particular artist is from my old stomping grounds, and I've been to all the places he mentions getting his materials from....As I've experimented with dorodango over the past few years, I'm struck by how these objects, created from such humble material, are nearly the perfect expression of process refinement.
Here's a bit more info about this art form.