I make one off hand built vessels. I use stoneware clays and once fire the pieces in sealed Saggars which I pack with locally foraged seaweed and oyster shells.
The surface effects are created in the firing process by the action of the salty seaweed and shells on the clay surface. I reduction fire in my gas kiln.
"The rough clay, the apparently careless handling, the effect of the organic materials all contribute to a knowing, primitive naturalness." Betty Blandino.