Wood-fired vase by Rick Devoss

An anagama kiln at a high school? That seems highly unlikely, doesn’t it? Many high school art teachers feel lucky to have a wheel and a small electric kiln. But Council Bluffs, Iowa, high school art teacher Clay Cunningham was determined. And with careful planning and execution, he, his students and some local potters made this vision a reality (and with great results, like the vase at left by student Rick Devoss).

 

Today, in an excerpt from the July/August 2009 issue of Pottery Making Illustrated, Clay shares the process and plans for building the “High School Anagama.” – Jennifer Harnetty, editor.

 


 

 

Two layers of concrete block form the foundation and raise the kiln to a workable height. Students build the walls and begin the stack.

Where There’s a Will, There’s a Way

 

When I first began planning the construction of an anagama wood kiln at Lewis Central High School, the Council Bluffs, Iowa, high school where I teach, many eyebrows were raised. Other potters said that it’s just not done at the high school level, administration voiced concerns and the students expressed surprise for the most obvious reason-excitement. Despite my own enthusiasm, we spent a year planning the project not only to increase safety, but to ensure the project’s longevity.

 

Workshop Format

 

I decided to direct the project in the form of a summer workshop in June. I planned a single-chamber kiln that would have great atmospheric potential, yet would fire over a weekend during the school year. As this is not a university, the students and faculty need to be in classes six straight hours a day, everyday. With a healthy mix of eight adult potters from the community and ten students from the high school, we had plenty of able hands, as well as a safe and constant adult/student firing team. Instructed as a three-week course, we spent the first week building the kiln, the second week making pots and sculptures, and the third week loading, firing and cooling the kiln.

 

 

A concrete block wall helps bear some of the weight of the roof and is placed 4 inches from the sides. The gap is later filled with pea gravel.

Building the Kiln

 

We began by laying out a 15-inch high foundation of cinder blocks, on which we placed 9 inches of K23 hard brick in an alternating header and stretcher fashion, to create a total interior floor plan that measured 45X96 inches. The first three feet of the interior were reserved for the firebox with the remaining five feet, tiered up 6 inches, for the ceramic ware. The flooring in the firebox area was constructed with K26 hard brick to better withstand the Cone 10 temperatures we would be reaching. Similarly, the walls were constructed 9 inches thick in an English bond (alternating courses of stretchers and headers) to a shallow height of 15 inches.

 

To create the domed roof, dirt is mounded and contoured then covered with plastic-a method borrowed from Fred Olsen's The Kiln Book. Castable refractory is applied over the form.

Before adding the arch, we lined the outer walls of the kiln with cinder blocks to a height of 37 inches, then filled the blocks with rebar and mortar mix. The small 4-inch gap between the cinder blocks and the hard brick was then filled with pea gravel to support the force of the dome on the kiln wall and to increase insulation and to allow for thermal expansion. The exit flue to the chimney was created slightly oversized at a total of 18X18 inches with the chimney interior at 12X12 inches. The chimney was built to a height of 15 feet with hard brick and finished with a 4-foot stack anchored with cables into the ground on three sides. A spanner brick was placed above the damper and it could also be removed to act as a passive damper.

 

The Roof

 

Instead of making a wooden frame for the arch, we created a solid mound inside the kiln, made from excess dirt from the construction site at a nearby middle school. With a couple shovels and a lot of muscle, we piled on two truckloads of dirt to form a smooth curved dome. Once shaped to our liking, we then mixed high refractory castable to form the dome. Since we were on a budget, all 2400 lbs. were mixed by hand with a hoe and mortar tray. We mixed the castable until it was the consistency of thick concrete and able to keep its shape when formed into a ball. Next, we lined the dirt with plastic bags and added one ball right on top of the other until the entire dome was completed to a thickness of 9 inches. Using two plastic buckets, we added the balls around the buckets so that when the buckets were removed, we had negative spaces for side stoking. After the last ball, we covered the entire dome with plastic bags to let it cure overnight. The next day we lined the dome with fiber blanket and an adobe mix of mortar, dirt and straw. This not only further insulates the kiln, but also protects the castable from the snow and rain.

 

Plastic buckets were used as forms to create side stoke holes in the roof. A fiber blanket was added then the roof topped with an adobe mix of concrete, mud and straw.

Note: As a safety precaution, everyone wore face masks and rubber gloves while handling the fiber blanket, as the small particles can irritate the lungs and the skin. Rubber gloves are recommended when handling adobe as well. The concrete mortar can irritate skin (and it makes your fingers pruney). After the castable set up, the door was disassembled and the dirt was removed. At last, after five days, the construction of the Lewis Central Anagama was complete.

 

Making Work

 

The next week was spent making a wide variety of work for the kiln. I provided three different clays to use with maturing rates from Cone 6 to Cone 10. In addition, a variety of tried-and-true high-fire glazes were supplied from copper reds to celadons and shinos. Students were encouraged to keep good notes of which clays and glazes were used for each piece to reflect on successes and learning experiences.

 

 

Firing steadily for more than 30 hours, the kiln reaches Cone 10. The kiln is allowed to soak at that temperature for a few hours, then it's sealed to allow it to cool slowly for a few days.

Getting Ready

 

Over the weekend, we spent one full day loading the pieces into the kiln. Tumble stacked one on top of the other, nearly every nook and cranny of the kiln was used. By Sunday, the front of the kiln was bricked up, leaving a main stoke hole and primary air inlets at the bottom of the door. Using a homemade block of castable, a U-bolt, an eyebolt and some chain, we were able to suspend a movable door from a post and lintel so that wood can be stoked with minimal heat loss. The post and lintel were made by setting two 8-foot 4X4 posts with a 10-foot 4X4 post for the horizontal beam and securing them with metal brackets. With the door in place and the kiln full of work, we were ready to go.

 

Firing

 

The kiln was started with a small fire at 5 PM on Sunday. By early Monday morning the kiln was nearing 1800ºF. Working in teams of two or three and stoking several split logs at the end of every reduction cycle, the kiln climbed to 2200ºF by Monday evening. We were at Cone 10 by noon on Tuesday and held it at that temperature until 5 PM when we sealed the kiln. To ensure a slow reduction in temperature, we dipped newspapers into a large barrel of slip and completely coated the entire kiln with the dripping wet sheets to decrease heat loss. This, as you can imagine, was a fun and messy highlight of the entire experience.

 

 

<p>View of the kiln interior and the stack of ware, showing some of the 400 pots included in the inaugural firing.</p>

The Results

 

After three days of cooling, it was time to open the kiln. The old adage of a kiln unloading feeling like Christmas morning could not be more apropos. All of the students, young and old, came early to see their approximately 400 newly finished creations and enjoy a potluck meal with a new family of bonded potters. We had much to celebrate. We were able to load and fire the kiln in the course of a weekend with just under 2 cords of wood. We proved that an anagama is not only doable at the high school level, but an amazing learning tool that will provide students with a life-long experience. We will be firing it up again this summer and our pottery club is in full swing to fill the quota.

 

Clay Cunningham is a ceramic artist and instructor, currently teaching at Lewis Central High School in Council Bluffs, Iowa. To see more of his work, or for contact information, visit www.claycunningham.org.

 

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