View Larger Image “Square Box,” 6 in. (15 cm) in height, thrown and altered stoneware, crackle slip, pattern and space detailing in black, wood fired, $225, by Sheila Clennell.

April 18, 2007

Green Wood and Its Effects in Wood Fire Kilns

by Tony Clennell | Read Comments (1)

Sometimes we think that to be new and exciting we have to change everything about ourselves.

Two consecutive events contributed to the ash-glazed Celadon pots that I am currently making and firing in our wood kiln: First, I attended the “The Naked Truth: International Wood-Fire Conference” in Cedar Rapids, Iowa, in September 2004; then I was invited to participate in “Ron Meyers and The Royal Canadians,” an exhibition that opened in December 2005 at the Signature Gallery in Atlanta, Georgia.

At the Naked Truth conference, I sat through slides and presentations of wood-fired pots from around the world, and saw surfaces that were out of this world. I did, however, wonder if I mixed up the slides and showed them out of order, would I be able to identify the makers? There were certain makers’ pots with which I am very familiar and could pick out of a police lineup with almost 100% certainty. The work of Linda Christianson comes quickly to mind; the forms are the signature and not necessarily the heavily encrusted wood-fired surfaces. The surfaces I saw, I loved and lusted for; however, I felt the identity of the maker seemed somewhat secondary to the surface created by the fire. In many cases, these surfaces were created by firing the pots for days, weeks and sometimes multiple firings of days and weeks.

Knowing that my wife and partner Sheila and I were not up to the task of days and days of firing, I wondered “why are we wood firing anyway?” There are a number of reasons, beginning with my love of fires and manual labor. Maintaining a wood-fired kiln has always been something I have done that few others around me did. So when wood firing became the “thing to do,” I switched to a train kiln that created heavily encrusted wood-fired pots in a relatively short period of time. But, attending the Naked Truth conference made me realize that the surfaces that I was creating (what I thought to be “nasty” crusty surfaces) looked like fine china compared to the surfaces I saw at the conference. My surfaces were fairly tame comparatively. If I wanted to make pots with that nasty surface, I’d need to be associated with a college or switch gears.

I ended up switching gears. My friend Ron Meyers of Athens, Georgia, asked Sheila and me to be in Ron Meyers and The Royal Canadians. The exhibition had a line up of prominent Canadian potters including Bruce Cochrane, Walter Ostrom and Matthias Ostermann, as well as Meyers. We wanted our work for the show to be wood fired so that it could be altered and enhanced by the power of the flame. I set out making a bunch of very loosely thrown, unglazed bottles and vases, and had two quite-nice wood firings. But when I sat down to really look at the work, I thought about what had occurred to me at the Naked Truth conference. How would anyone know these pots were made by me? They could have been made by lots of different wood-fire potters. Where was my signature?

My fellow Canadians’ pots would be easily identified and Ron’s animated images would certainly be instantly recognizable. Sheila had not panicked and was quietly working away making work that she was familiar with. She seemed content to make small refinements and was busy paying attention to details. Her work, to those familiar with it, would have her name written all over it. I realized that maybe the unglazed, crusty wood-fired surfaces just weren’t my signature. Although I loved to look at those rich surfaces I saw at the conference, they weren’t what I needed to make.

Fearing that I might be the weakest link in the show, I returned to what I considered to be my signature piece: the jug and the clay handle. Handles have always been my signature and I decided to make work that showed them off. To best show off the forms and the handles, I picked a glaze that I have long loved for its ability to pool and run. I had abandoned the use of this glaze long ago because it often gave me trouble in the gas kiln by running too much and sticking to the shelves. I made the forms so that they had what I call a “European foot,” which acted like a saucer to catch the glaze and ash as it cascaded down the exterior of the pots. True to my form of testing, I fired the whole 75-cubic-foot wood kiln with this glaze on every piece. The pots were wadded underneath and, with my European foot, I figured they would be fine.

Early in the firing, at about 1800°F (982°C), I added green wood to try to hold the kiln back. The kiln slowed down and demonstrated signs of reduction with the green wood. Later on, the front of the kiln reached Cone 10 while the back of the kiln was quite cool. I decided that, in order to keep the front from overfiring while I stoked the back of the kiln, I would add green wood to the firebox again. My original thinking was that this would slow things down while everything caught up. Much to my surprise, the front of the kiln skyrocketed to temperatures of Cone 12 flat and more likely Cone 14 plus. I thought the ash glaze would just run like a river all over the shelves, but there was no turning back. We finished off the kiln worrying about shelves warping and bending, and glazes pooling everywhere but on the pot.

After an anxious two-day wait, we opened the kiln. The pots were more than fine. In my mind, they were beautiful. Although the wood kiln reached temperatures above Cone 14 in spots, it was slower and gentler. The glaze had a depth of surface to which I’m afraid my photographs can’t do justice. The additional ash from the wood kiln could be seen flowing down the windward or flame side of the pot. The cooler side of the pot was a soft satin matt. We unloaded the kiln and I wrote in my kiln diary, “Green Wood?????!” Sheila’s pots, although not all green, were spot on!

To find out what was going on with this green wood, I sent the following message to my friend Nils Lou, author of The Art of Firing, an experienced wood-fire potter and associate professor of art at Linfield College in McMinnville, Oregon.

We are now firing our kiln with green wood at lower temperatures (Cone 06) to obtain glaze reduction and also at higher temperatures to send heat to the back of the kiln in the form of steam and to improve reduction. As for the use of ash in a glaze, it can be said that the simpler a material is, the more complex its molecular makeup. The fact that ash on its own makes a glaze suggests that it must be a very complex material. The use of a glaze that contains two or three materials suits my personality. Just altering these three materials can make all the difference in the world.

Since we work in Canada’s best-known wine region, we are very closely linked with the wine industry and its way of thinking. A wine snob can tell the difference between a Beamsville Bench Chardonnay and a Napa Valley one. The soil, the type of vines, the season and the overall climate of the region combined with the winemaker can produce a wine of a distinct nose, taste and quality. I would like to believe that the addition of local materials to the ash celadon glaze makes it as distinctive to the Beamsville area where we live, as the one you might produce in your part of the country.

People new to ceramics often ask how a potter comes up with their own identity and their own signature in their work. For me, the answer with this green-wood work was the rediscovery of an old love; looking at the things you love and the things you do well and trying to pull that together into something that speaks of who you are. If I was asked into another show, the first thing I’d do before throwing and firing two kiln loads of wood-fired pots is sit down and answer these two questions: Who am I? What kind of work expresses best who I am? Sometimes we think that to be new and exciting we have to change everything about ourselves.

The pot is the man, his virtues and vices are shown therein . . . no disguise is possible.—Bernard Leach.

Once again the wisdom of my old reference Bernard Leach has penetrated the gray matter of this brain of mine. The pots you make must be honest to who you are and you can’t just change them like you were off to a costume party. Unless of course, you see an invitational show as a costume party and not a representation of what you’d like to wear each and every day.

After looking at photos of our work, one should hopefully see a respect for function. Our work is meant to be used. The pots ought to display strength, since I think a couple making craft in this century ought to possess inner strength. The pots ought to display skill and yet a relaxed, comfortable use of that skill. We have been making pots for several decades. The pots ought to have attention to small details. After all, it is the details that make the difference between a professional potter and an amateur. The pots ought to inform you of what colors we are most likely to be wearing today. If you guessed plain, drab or green you answered the skill-testing question. Finally, the pots ought to show a marriage, two people working together, similar but different.

Students achieving oneness will move ahead to twoness.—Woody Allen

Dear Nils,

I have written this article for Ceramics Monthly explaining the phenomena of what I experienced with green wood. At about 1800°F (982°C), I was having trouble holding the kiln back. It just kept rocketing ahead, and I was trying to establish a reduction atmosphere. As a last resort, I added green wood, which not only slowed the kiln but established strong signs of reduction. After two hours of green wood reduction, I fired as per schedule with dry wood until we hit Cone 10 in the front of the kiln. In order to hold the front of the kiln at Cone 10 while we sidestoked the back, I added green wood. Much to my surprise, the front started to rocket higher and higher. What’s goin’ on?

Best,

Tony

Dear Tony,

In my opinion, the green wood has the added potential energy of having the water breaking down and releasing hydrogen at elevated temperatures above 2200°F (1204°C), which can then theoretically produce more Btus (British thermal units) and a reduction atmosphere as well. Your initial thought of green wood slowing down the temperature is natural common sense because that would likely happen in a wood stove environment with temperatures below 1800°F. It probably depends on the size of the wood with smaller, split pieces releasing the water vapor more readily than the larger logs. The anecdotal evidence that you have given seems to bear out the fact though that green wood can indeed work to increase the temperature.

Best regards,

Nils