Firing Methods and Results
Pit Firing
Generally speaking, pottery that is referred to as
being pit fired, is not glazed, and has been fired in an open bon-fire or
primitive pit kiln. |
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Terra Sigillata (
a liquid clay) is used to seal the pot's surface.
The technique predates the development of glazes.
Pre-Columbian pottery as well as Greek Attica wares used Terra Sigillata |
Robert applying Terra Sigillata
with a brush to an unfired pot. He then uses a soft cloth to buff the
surface, compacting the fine clay partials, and producing a polished
surface. |
Pit Firing
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Pit Fired Pottery
is an imprecise term. 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.
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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. |
The Process of Pit Firing
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Pots in Sawdust
Where pots come into direct contact with sawdust, a deep black color may
develop from carbon trapping. Fine sawdust produces deeper blacks. |
Copper and
Salt
Copper is added to encourages a rainbow of colors, from deep red to blues and orange.
A small amount of
salt helps with color development. |
Wood filled Pit
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. |
Burns to
Coals
Roberts firing method involves filling
the pit with wood and letting it burn. Some potters do not add as much
wood on at the beginning , then stoke the pit during the firing. |
Pottery in the ash
Pots taken out of the pit have a small amount of ash clinging to their
surface. Ash is removed using soft brushes
so no damage is done to the pots surface. Then a sealer applied to
protect the finish.
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Surface Protection for Pit Fired Pottery
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| The black
areas are the result of carbon trapping from sawdust, the bright colors
derive from copper in the flame patterns. Ash will be removed gently to
prevent scratching the pots surface, then a hot wax sealer used to
enhance the colors and seal the surface. |
Once ash is removed, the still
warm pots are coated with butchers wax , which melts into the porous
surface, and is then polished to a high gloss. |
Durability of Pit Fired Pottery
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Pit Fired Pottery
Pit fired pottery, is unglazed and fired to a
low temperature, there fore it is porous and not watertight.
The colors developed on Pit Fired pottery are not fused in a glass,
as they are in a glaze.
In many ways these pots should be thought of as a painting
created
by fire and smoke. Their color could fade if placed in direct sunlight for long periods. |
Carbon Trapped
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Carbon Trapped
or
Smoke Fired
In the American South West, black on black
wares, made famous by Maria Martinez in the early 20th century, have been
developed to a high form of art. Such works attain great value in the
collectors market. The kind firing done by native
American potter 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 for the organic
matter which produces the smoke. The manure is applied in large quantities
directly on the fire and
immediately covered with dirt. This smolders the fire and
impregnates the pots with black carbon. |
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05/14/13
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