This process is called 'naked' because it has no glazed surface. The black and white patterning is achieved by applying a liquid clay over the piece, placed in a small kiln, and fired to 1500 degrees. It is then removed while still hot and placed in a closed container with paper and sawdust to create smoke around the piece. The final surface is coated with a crystalline wax to give a satin smooth finish.
This piece is right out of the kiln and has been smoked. The sacrificial layer of slip applied to create the black and white patterning is being scraped away to reveal the original surface.