I've only done it the Native American way. Barbara Gonzalez
had us wipe a thin layer of slip on the pot and burnish the damp slip
till it shined. The pots were reddish brown before they were fired.
We fired them in a open fire surrounded by dry cow chips. Then the
fire was totally smothered with powered horse manure so no air
could reach the pots. They came out a glossy black. A beautiful
Woody, Retired in Albuquerque