Firing Methods and Results
few working potters use wood as a fuel for making pottery.
The process is demanding and requires a great deal of time. Intensive
labor is needed for preparing wood, as well as, maintaining and firing the
Some potters use wood for ecological reasons, however most choose wood firing
because of the effects achieved from fly ash and flashing.
Wood firing is not the easiest method for producing matching wares. It
is best utilized by potters seeking unique & natural process driven
surfaces, which result from firing with wood as a fuel.
Wood Firing Process
Noborigama consumes 6 cords of
wood during 40 hours of constant stocking. He uses a blend of woods
including Pine, Spruce, Hemlock, Oak and Maple.
softwoods produce a faster hotter firing, while hardwoods aid in keeping a
bed of coals in the firebox.
Depending on the stage of the
firing, stoking may take place as
frequent as every 3 minutes. The potter must pay close attention from the first stoke of wood to the last.
Reaching the 2400 degrees F. necessary for a firing is not dependent only on the amount of wood
burned. It is also the timing of each stoke, the size & species of
wood, as well as the moisture content, that makes a
A kiln firing that reaches the desired temperature is no
guarantee of success. Variations of flame and ash flow are impacted
by how the ware was stacked prior to firing.
Wood Firing Process
Wood Fired Pots
are stilted on "wads", which gives a distinctive blush of flame
under the pot. This is an easily recognizable mark of the firing process. Wadding prevent pots from becoming fused to the kiln shelf or to each
other if "tumble stacked".
In wood firing, wadding
may be mixed with sawdust, flour or coffee grounds. These organic
materials burn out during
the firing making the wadding crumbly and easy to remove.
Wood fired pots are engulfed in a river of fire. The marks left as the fire
flows around the
wads will occasionally make patterns referred to a "comet trail' (shown
to the right).
Wood Firing Styles
Robert fires most of his work in a Noborigama
kiln which is most appropriate for pottery that has glazed surfaces.
Firing this piece on its side, Robert,
incorporated the wadding patterns as a surface feature.
kilns were developed when potters began to refine their glazing methods. This
style of firing allows for more control of the temperature, and better wares
with functional surfaces.
Wood fired kilns gave way to gas and electric in the 20th Century, as
industry demanded more consistency and refinement of glazes.
Studio potters, such as Robert, fire with wood
to seek the various peccadilloes caused by ash flame flashing, while still
producing functional surfaces for tableware. The pot above has a Korean
celadon glaze with great variation from the wood firing.
Anagama firing is an ancient method
usually done (as shown on the piece above) without glazes. Anagama firings
are very long, often going on for many days or weeks.
The process of burning such a huge amount of wood creates large volumes of
ash, which melt to produce a rudimentary glaze surface.
Most anagama fired pots are not functional by western standards. The
pieces are prized more for their sculptural or decorative value.
Wood Firing Effects
is not unusual for wood kilns to have a wide range of temperatures
a single chamber.
The pot above received a large about of ash, and was
in a cool region
of the kiln which produced this matt surface.
| Tiger Eye
The glass bead which formed on
the rim of this pot, shows what can happen when high temperature fuses
fly ash creating liquid glass.
This pot was fired on its side,
encouraging the ash to flow down the rim. The three wad patterns are
clearly visible on the side of the piece, surrounded by a halo of rose
color flame flashing.
Wood Firing Effects
|Ash & Gases
pots in a wood firing are affected by ash in subtle ways.
The flow of gases and ash increases the fluxing action on the windward
side of this piece, it exhibits patterns of
oxidation and reduction.
clay slips to pots promotes flashing and encourage
the development of certain colors.
Pottery coated with slips and fired over a moderate length of time,
produces quiet and gentle effects.
|Large amounts of fly ash, and high
can create a natural yellow glaze.
|The pot above received a thin coat of "white
slip" prior to firing.
Without the slip, the clay body would have been dark brown.
Patten on Floor
|Six Week Firing Cycle
Glazing a kiln load takes about 14 days and another 12 days to wad
and load the pots. Actual firing time is 42 hours ten another 4 days of cooling before
The floor of the glaze ware chamber of this kiln is shown at right.
The main firebox at the far right and the salt chamber on the far
left. Toward the end of the firing a "dragons tail" flows out the top of
the chimney. Photo was taken 33 hours into the firing.
Unloading, cleaning wad debris, grading and pricing pots adds another
20 days. This kiln is fired twice a year, usually in June and September.
When the first chamber of
Robert's Noborigama reaches temperature, stoking ceases in the main
firebox. The second chamber (salt chamber)
continues to be fired until it also reaches
This results in ash being pulled from the firebox into the first chamber
as the glazes are cooling. Note the black pattern on the floor of the
Since the main firebox is no longer being stoked, the glazes (in the
first chamber) stiffen and ash drifting onto the pots will not melt,
producing a dry stone-like finish. A small number of pots in each firing will be re-fired
later to melt this ash and improve the surface quality of the pots
The greatest volume of dry ash is
nearest the bag wall. The dry, kiln cooling ash, only occurs on the floor of the kiln.
Pots located on shelves above the floor are unaffected by drifting ash
once the firing is completed.