Although the exact origins of this technique are not known, pots showing this effect began showing up about 30 years ago utilizing burnishing techniques developed by Pueblo tribes of the Southwest.
Each of these pots have been thrown on the wheel, smoothed and trimmed. After drying, thin coats of terra siglatta, a very fine clay slip are brushed on, and polished to a silky surface.
After the pots have been through a bisque firing they are reheated to approximately 1000'F and taken out. Horsehair and feathers are then laid across the pot, leaving their carbon imprint on the surface.
After the residue is cleaned from the surface of the pots, they are warmed, and waxed with beeswax polish.
Like raku, these pots are not watertight and should be kept out of direct sunlight.