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Christine Homer Weaving

Firing Methods and Results
Wood Firing

 Relatively 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 kiln.

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.

Generally speaking 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 great fire.

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.

 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).

Noborigama

 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.

     Noborigama 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.

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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.

Variation

It is not unusual for wood kilns to have a wide range of temperatures
within 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.

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.

Glazed 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. 

Appling 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.

Glazing a kiln load takes about 14 days and another 12 days to wad and load the pots.The actual firing time is 42 hours with 4 days of cooling before unloading.

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.

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 affected.

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.