You often hear the phrase, ‘that’s a good question’, during an interview. It seems to me that in replying this way, the person interviewed is not only flattering the questioner, hoping to make for a friendlier situation, but also it gives the interviewee a chance to think. One of the first questions asked of a woodfirer is ‘Why woodfire?’ followed by ‘What particular effects are you seeking’? There are many such questions concerning wood-firing, and we need to consider these questions carefully. It is not just a matter of vitrifying the clay—although that, for me, is an important part of the process—it is the end result, what we say with the work, how we show our sensitivity to the process, that counts.
I have a number of kilns for wood-firing, built during the past 20 years or so, gradually assembled for different needs, to accommodate different types of wood, or to experiment with ideas. My Bourry box style kiln gives well vitrified effects with salt but the results seem too clean, not enough evidence of the process, of the effort in lifting logs over the burning chamber of the firebox. The Phoenix fast fire kiln has a generous capacity, and after attaching a door to the firebox, is no longer so hot for the firers. I have trouble making this kiln reoxidise; it is fast cooling as well as fast firing and using my clay body, the pots seem insipid in colour. The other problem with this kiln is that it has the heat concentration where it needs strength, and after many firings the floor of the kiln is deteriorating. A trolley kiln for wood-fired salt was my next addition. Of German design, it is easy to load, has a good 80cu.ft. capacity, and the ash and salt circulate all through the kiln and settle on the pots. Firing to cone 10 is not a problem with this kiln. One surprising fact for me at least, is that the kiln seems to have shrunk away from the door, leaving a gap when the trolley (with door attached) is pushed into the chamber of the kiln. I have been chipping and nibbling away at bricks on the edges of the chamber and the trolley, at the same time as repairing the walls, trying to make a better fit. Peter Korompi, the Hungarian potter, helped me build this kiln. Please come back to Gulgong Peter, from Kecskemét or wherever you are, this kiln needs your help, not surprising after hundreds of firings. My tunnel kiln, a type of anagama, with a chamber five metres long, an extended flue (secret chamber), and usually fired for a period of three to four days, has been fired twice a year for at least 12 years now. The latest addition under the kiln shed roof, a broad-chambered kiln, shaped like a racing car, designed and built by Fred Olsen with a team of helpers at ClaySculpt Gulgong, is in regular use. It is these two last kilns that give rise to all the questions—how and best to fire for the clay, for the forms, for the effects.
In the days running up to Christmas 1999, I fired the racing car kiln with the help of my two trusty members of the team, Ken Horder, a Newcastle, NSW, potter, and Judy Boydell, a Sydney potter. We have been firing together for more than 15 years, we know each other’s strengths and we work together well. For this particular firing I wanted to throw moderation out of the window and go for a more extreme result. Ten hours were added to the usual length of the firing and an extra tonne or so of wood consumed. I wanted this time, to discover what heat we could produce and how this would affect the wares. I had gathered sufficient wood from fallen timber on the property, narrow in diameter, and of a good length to fill the full length of the firebox. This kiln has a wide firebox, as wide as the chamber, nearly two metres across, a wide chimney and generous flue openings. These features make the kiln easy and fast to fire, but not so easy to obtain a strong reduction. My idea of firing longer and harder, was to force a more pronounced reduction and therefore colour in the clay, and to show more the effects of the ash and flame.
Four stoking ports in the half-way section of this kiln’s stacking area give the opportunity for greater control and ash effect. The stoking ports at floor level assist in the temperature gain at the rear of the kiln, while the ports over the stacking chamber give localised ash on top of the pots themselves.
We each had pieces in the kiln, some of them were glazed, some pieces were raw unglazed clay. Pots were on shelves or tumbled-stacked beneath the stoke holes. There was a good mix of sizes and shapes, The work was all placed on wads composed of a mix of fireclay and alumina. Three cone sets were placed, one each side and visible from the two upper stoke holes at the back, and one set was placed on a shelf at the front, visible from the front stoking port. The cones I use are always the same: 06 for the start of reduction, cone 2 for another burst of reduction, and cones 8, 9, 10 and 11, to monitor temperature rise. It was just getting dark as we bricked up the entrance of the kiln, leaving a gap of nine bricks for the firebox stoke hole and a slightly smaller gap below on the floor for the warming fire.
I have been known to be a little too impatient to take responsibility for the first shift. Just cleaning up old wood and lumber, gradually clearing the area, raking the ground around as I go, and suddenly the kiln is at red heat or more. However, on this occasion the first shift was mine. It is a quiet time, a small fire at the front of the kiln is a gentle warming operation. The radio is set to classic FM, there are books to look at and tasty snacks to share with the dog. At 2 am I go to find Ken. “Wake up, your shift” I say. “Thank you” he says and I wonder if he means it.
Three mornings this is repeated, Ken still saying a polite ‘thank-you’ each time as I disturb his sleep. Judy takes over at 6 am and so the day goes, four hours concentration on the kiln, while the other two either rest or mooch around organising food, bringing wood from the wood pile, or gathering or chopping small pieces of wood for side stoking. When cone 06 melts at the front, I push the dampers in to one third open, and start to use heavier logs. My clay body needs a strong reduction to give colour. The kiln is held in reduction for at least two hours at this time, and the smoke from the stack is dark and heavy. When cone 06 is bending at the areas under the stoke holes, this heavy reduction is repeated. As all woodfirers know, the kiln is continually moving from reduction to oxidation and back again. I try to keep the kiln in active reduction during the cone 06 to cone 2 period. I have a gap in the chimney so that I can watch the flame pattern and colour. When I can no longer see the flame, it is time to stoke again. After 20 hours of firing there wasn’t a cone visible anywhere. But I wanted to continue and it was only after another 40 hours, and perhaps a total of five or more tonnes of wood, that we called a halt. The wood was mostly eucalyptus, with some pine plus some wattle which we joked about as we used it, talking about adding layers of exotic ashes to the wares. The eucalypts, mainly yellow box, red gum, stringy bark and iron bark, all have high calorific value and burn away to a fine ash. There is never much residue to be seen in the firebox after the kiln has cooled.
As to the results—well, that’s a good question. We certainly reached a high temperature, cone 11 was not recognisable in any of the sets of cones, but had melted away to nothing. The colour of the pots was good. The ash on the wares was overabundant. The porcelain was flashed pinks and oranges. Our wadding was quite inadequate for such an immoderate firing—much larger wads and a more refractory mix are needed for a firing of this type. Many of the wares were permanently attached to the floor of the kiln or to the shelves, that is until they were broken away. Much of the porcelain had slumped, more than what could be called an elegant or lyrical warping. The desired matt yellow ash of eucalyptus was deposited on many of the pieces and some of the glazed wares had a rich depth to them. The pieces in the two ‘gun’ spots, at the corners at the front of the firebox, showed much of what woodfirers treasure: the black of charcoal, the grey texture of sintered ash, the gloss of melted ash and the red of the reoxidised clay body.
So how soon can we fire the kiln again, we ask ourselves. A good question but easily answered—as soon as we can. The extra time and temperature gave the work an added dimension, a method which we will repeat but, with experience, we will be prepared for the flows of melted ash, and the porcelain forms will need to be sturdier. And I did buy myself a bench grinder for Christmas to rescue some of the pieces from this firing, my memorable last for the 20th century.
Janet Mansfield 2000
Issue 1 2000 The Log Book