Crack pots
The name "Crack Pot" is derived from the method of construction.
Have you ever been rolling out pastry and found the surface cracking? The surface has dried and therefore can't stretch as far as the underneath. Its the same with a clay block that has had its top surface blasted with a heat gun prior to rolling into a slab.

Rock Pots
Have you ever been to the seaside and seen seaside rock being made? The thing about seaside rock is the name goes all the way through I am using this concept to make my Rock Pots .I make my rock slice it up and put the pieces together to make a slab and then use that to make my piece.
As might be expected there is an Ancient Japanese technique called Nericomi or Neriage which does the same.