Generally speaking, pottery that is referred to as being pit fired, is not glazed, and has been fired in an open bonfire or primitive pit kiln. Pottery fired to this low temperature is porous and not watertight.
Terra Sigillata (a liquid clay) is used to seal the pot’s surface. This technique predates the development of glazes. Pre-Columbian pottery as well as Greek Attica wares used Terra Sigillata.
Pit Fired pottery is an imprecise term, which is generally referring to an open fire, often without a kiln like structure.
In an open fire, the potter can only expect to attain a temperature of 1500 F. This is adequate for hardening earthenware, and is commonly employed in primitive societies.
Contemporary studio potters use pit firing to attain specific surface effects, such as Carbon Trapping and Color Fuming.
Few potters, who specialize in pit firing, use the process for functional wares since the pots are not glazed and porous.
When pots come into direct contact with sawdust, a deep black color may develop from “carbon trapping”. Fine sawdust produces deeper blacks.
Copper is added to encourage a rainbow of colors, from deep red to blues and orange. A small amount of salt helps with color development.
The firing takes 16 hours. Robert stacks wood directly on top of the pots, but uses care to evenly distribute the weight of the wood.
Roberts firing method involves filling the pit with wood and letting it burn. Some potters do not add as much wood at the beginning , but rather stoke the pit during the firing.
Pots taken out of the pit have a small amount of ash clinging to their surface. Ash is removed using soft brushes, to prevent damaging the pots surface. A sealer is applied to protect the finish.
The kind of firing made by Native American potters is done in an open bonfire, producing a type of pottery known for “carbon trapping.” The deep blacks result from the heavy smoke generated at the end of the firing when the hot wood coals and pots are smothered with organic matter.
Typically dried horse manure is used and produces a great deal of smoke. The manure is applied in large quantities directly on the fire and immediately covered with dirt. This smothers the fire and impregnates the pots with black carbon.
In the early 20th century, America South West artist, Maria Martinez, developed beautiful black on black pottery that was recognized as a high quality art form. Her work attained great value in the collectors market.