The Naked Truth: 2004 International Woodfire Conference
Confessions of a Female Woodburner
By Karen Terpstra
In 1991 I was told not to attend the Woodfire Conference at Iowa City in ’91 because it had nothing to do with my work. I was warned, “Karen, It’s just a place where men hang out pretending to be macho, throw a few logs of wood in a kiln, sit around and drink beer, smoke cigars, and tell dirty jokes. You will be better off staying home and making your lowfire work.” And, if that weren’t enough, two guys in my ceramics class were encouraged to go. If I had to learn to smoke cigars, drink beer and tell dirty jokes it was not going to keep me from woodfiring.
After eighteen years in the interior design field, I discovered the color palette of lowfire glazes on earthenware. Soon I was coordinating color and pattern with glaze on ceramics. In 1993, I was accepted to the MFA program at the University of Iowa for my portfolio filled with colorful abstract forms in earthenware with lowfire slips and glazes. Of course, Chuck Hindes told me I was accepted to the program only because he discovered my husband owned an English Setter (as did he) and had several places to hunt pheasant in central Iowa—he was kidding, of course (I think). Little did I know at the time that I was entering one of the most prestigious schools in the country for woodfiring.
I was at the U of Iowa for about a week before I could actually pronounce the word “anagama”– another two weeks before I learned the word, “naborigama”. I had no clue about the process of woodfiring. I looked at that big, scary thing (the anagama) right outside the door of the studio and couldn’t even figure out where you put the wood, let alone figure out how you got the ware in there. Someone said, “Oh, you just stoke it from the front firebox; the flame goes through the pots to the end of the kiln and smoke goes out the chimney.” “Huh? What?” I mused. Yeah, right.
Hundreds of brown pots came out of the wood kilns that semester. Someone pointed out that “brown” included subtle shades of gold, yellow, green, gray, a bit of orange and burgundy, but I saw all that brown and “brown-with-subtle-color”. Not impressed, I continued with my brightly colored palette on earthenware and fired the reliable electric kilns. But, there was an intrigue. By late spring, and at the last minute, I decided to make something for the next firing. I had to find out what it was all about.
I had a series of nine, small horse heads and refused to let all of them go into the kiln without glaze despite the begging of my professor, Chuck Hindes. I had to put glazes on at least three of them so I would have something from the kiln I would like. Unloading day came and I was surprised to find nine horses with nine variations of browns that included gold, gray, orange, yellow, burgundy, black, white and an odd looking shino. I wasn’t sure about the way they looked. I didn’t know how to look at woodfired work. I hadn’t paid much attention to it before. Chuck kept telling me, “Don’t throw these away; don’t give anything away; you have to learn to appreciate this work.” Don Rietz had fired with us during that firing and with his and Chuck’s encouragement; I decided to add the challenge of the woodfired process into my work. More and more of my work became woodfired, less and less of it was lowfired, underglazed earthenware. Aaaaaagh! I was hooked on a challenge to find color in a wood kiln. This was a lesson I have not forgotten. People need to learn how to look at and appreciate wood fired work; not only a wood firer, but the clientele as well.
I landed a job at La Crosse. Right away the students convinced me to build a woodkiln on the small, outdoor space in back of the studio. I procured permission from the Department, the Dean, the Physical Plant—which included the health and safety director. I held a meeting with the directors of the physical plant, the city fire chief, and the zoning commissioner. With Jack Troy’s book, “Woodfiring Stoneware and Porcelain”, in hand, we discussed plans for building a small wood kiln on campus in the middle of the city of La Crosse. Jack’s book was influential with the examples of other schools with woodfire kilns. We made plans for a small train kiln and an advanced student did most of the work. It fired well for about two years. The students loved it, except for the fact that we couldn’t get enough work in. Everyone was fighting over kiln space. It was time to make a larger one.
It took me a little while to decide what kind of kiln I wanted to build; I researched every kiln book I could get my hands on. Along with Jack Troy’s book there was Fred Olsen’s “The Kiln Book”, Nils Lou’s “The Art of Firing” and several articles from magazines. Available space was limited and with an undergraduate program I needed a design that would be versatile and not too demanding on inexperienced students. A double-sprung arch seemed the best solution. It saved space for maneuvering around the kiln and gave us the most cubic feet per chamber. The only obstacle was figuring out how to tie the two chambers together without imbedding any metal framework. We devised a channel between the two chambers where the arches met in the middle. Air could pass through to keep the metal cool enough so the structure would stay sound and tight. I insisted on adequate insulation. We put in passive dampers on three sides of the lower part of the chimney. At the time I wasn’t sure how to use them, but thought it would be a good idea to add them while building, rather than later. What a good decision! The kiln is probably over-built, over-engineered; but, I was determined to build a kiln that would last my tenure at La Crosse without having to rebuild or repair. When I was told, “Oh, you don’t need an expansion joint in the floor.” I put one in anyway
By teaching the students how to stoke and what to look for in a flame, they get a pretty good idea of how to raise the temperature in the kiln. They learn how to control it with the passives, making the firings controlled and relaxed; it’s like fine tuning an instrument during a concert.
This is what I tell my students:
Candling:
Leave the passives closed (bricked up) when candling the kiln to warm up the chimney. This gives you time to figure out how long it generally takes for the smoke to go through the kiln and exit the chimney from the time you stoke. It’s always a good idea to keep track of that. In the first part of the firing, if the smoke goes through the kiln in less than 10 seconds, it’s drawing fine.
Body reduction:
I don’t do it. (I can hear collective gasps; “Oh my god, she doesn’t body reduce!”) We get enough reduction with our stoking pattern, which I will explain later.
Mid firing:
If things are going well when you want to start dropping cones, take a row of passive bricks out (in other words–one row of passives are now open). (Dyslexic people have trouble grasping this concept and also explaining.) As long is the draft is good–and it must be good, this will start to hold more heat in. When you know your kiln and crew, you can speed this up and try taking the bricks out sooner. We candle in as short amount of time as possible unless there is ungodly fragile work right up in front. When the bricks are pulled out of the passive openings, cold air rushes into the chimney and slows the draft. Too many bricks pulled out can cool the chimney and backend-don’t do that.
When the flame is running through the kiln, you want to keep the hot part of the flame in the chamber(s). If too much flame is coming out of the chimney, the hot part of the flame is in the flue and chimney and you are wasting precious fuel. Remember the hot part of the flame is in the middle-not the tip. I know, fireworks at night are fun to watch, but when you have neighbors, a city fire department, and fire codes…keep the flame under control. We can’t afford to waste fuel anyway.
During the time you are trying to raise temperature and knock down cones, you will encounter some stalls. These are our UW-L trouble shooting tips.
Predawn through early dawn:
This creates an atmospheric change (the barometric pressure drops) that always, always slows down the draft. As soon as you observe this, put the bricks back in the passives. Just keep the flames going through the kiln. It’s time to relax, keep an easy stoking pattern, watch the pyrometer if you have one, turn on the morning NPR news, fix a pot of coffee. Sit back and don’t worry about a temperature rise. It will not happen. Just don’t let it fall more than 100-150 degrees and get caught by the next crew. By 9:00 am. you should see the difference in the draft and the wood is burning faster in the firebox again. Take out the passive bricks again, hold in more heat and resume temperature climb.
Bad Weather and low barometric pressure:
If there is a cloud system, rain, sleet, snow and all that, you will have to work harder. Push the wood to the firebox without choking it and leave the passives closed (bricks in). This makes the chimney work harder to move the flame to the back or wherever you want it. The barometric pressure will be pushing down the chimney and tends to slow the draft. With this type of situation you will have a more reducing atmosphere which is a good thing. The bad thing is the rise in temperature is slower and you have to work harder.
High pressure system:
If you need to hold the kiln back, too much flame shooting out of the chimney, start pulling more passive bricks out. With high pressure systems here in Wisconsin we have to pull all the bricks out to hold the flame back. You may have to cut back on stoking.
Stoking Pattern:
We stoke as much wood into the firebox as we can without choking the kiln. Students learn to do this by watching the pyrometer. At this stage of the game, the pyrometer is an ideal learning tool. It builds their confidence. Pushing the wood to the limit in the firebox without choking it, raises temperature and gives us reduction. As we stoke, reduction is happening; then the atmosphere in the kiln and firebox begins to clear. When the firebox is clear it is oxidizing. Let it happen. It takes awhile, relax some more and just watch that temperature rise on the pyrometer! Too many people stoke too soon. That wastes wood and crew energy. When the temperature peaks, stoke again. The wood should be falling apart and it’s apparent that it’s time to stoke. With every stoke we have alternate reduction and oxidation.
Wood:
In my opinion it is difficult for beginners (or anyone) to fire in a short amount of time with green wood. We like our oak cured to the point where we start to see “checking” (little cracks perpendicular to the rings in the wood.). We have pine available in our area but choose not to use it since it causes way too much smoke on campus and makes us work too hard by doubling the amount of stoking we have to do. We do not use old wood. A former student once tried to fire with two cords of old, punky walnut. He couldn’t reach temperature and any minerals the wood once had were gone.
Soaking:
Put your inexperienced and tired people on a shift here and there during the soak. Anything goes. If the temperature drops 500 degrees, so what! You can recover during your allowed soak time and hey—another layer of color! We fire for 30 -36 hours which includes a soak of 8 – 10 hours, and try to keep the temperatures between cones 8-11. The passives should be set to where you are using minimal amount of wood to maintain the desired temperature; and this usually depends on the weather and how tight or loose the stack is.
Stacking:
If the kiln is packed too tightly you may have trouble raising temperature. Close up the passives (bricks in). You will need more draft through the chimney. With a looser stack, flames will have more of a chance to lick around the pots.
Shutting down:
We try for cone 11-12 everywhere and then just shut it down and don’t make a big “ta-do”. Sometimes cones 12 -13 drop early during the soak with a crew that lets it get away, but I don’t worry about it so much anymore. We just make sure we are at cone 9 or above when we shut down. As we are closing up the firebox and stoke holes, we leave the passives open to discourage any draft that will move any ash that might stick to the pots and not melt. We don’t mud up doors and fill every little crack-only the big ones. We were anal about making this kiln a tight one when we built it, so there’s not much to tighten up at the end. We clean up around the kiln and by that time the firebox has burned down, we shove in the mechanical dampers to hold in as much heat as possible.
We have two passive dampers on each side of the chimney and across the back. The chimney is wide at the base. We also have three mechanical dampers used to close down the chimney at the end of the firing. There are three welded frames holding steel mesh with kaowool buttoned to it. It’s the slow cool that’s important to us so it helps to keep that hot air in after shutting down the kiln.
We are consistently experimenting with claybodies, glazes, and flashing slips. We fire from 30 to 36 hours and use about one and a half cords of oak. The oak is cut from split “ends” with bark—throwaway stuff from the Amish. We split wood for the back chamber before each firing. I can’t stand the sound of the splitter while we are firing so we make sure it’s done well ahead of time. As I mentioned, we fire lots of utilitarian work so flashing with a light dusting of ash is important. Current favorites that come out of the kiln are porcelain pieces with flashing slips. We have lots of stoneware functional work with slips on the outside to help the color along a bit and liner glazes. We get a fair amount of ash on the first rows behind the firebox in each chamber so lots of sculptural work is reserved for those areas.
It’s true that it takes about a dozen firings before you learn your kiln and even after that there are always variables to take into consideration. We plan on a bit longer firing when weather is bad; however it’s no disadvantage for us since we seem to get a bit more reduction and great pots with the extra effort. With good weather and a high pressure system, the kiln flies, we have to hold back and not let it get away to cone 15. Many of the problems for a beginning wood firer and kiln owner are people problems. We have had our share. We have experienced guests at our kiln who fire as if they are firing their design with no regard to what it really takes to fire a “different” design. It not only messes up the work but confuses students. The firing crew needs to know who is running the show and just as importantly…kiln etiquette. Not much has been written in kiln manuals or instruction books about kiln etiquette.
I almost cringe when I hear someone say, “I want to build a wood kiln.” Too many people do not think about the details. What is your wood source? How long can you physically and mentally handle a firing? Are you firing alone? Who is the consistent and dependable crew? What type of work are you firing? Does the kiln determine the type of work or do your expectations of a certain woodfire aesthetic determine what kind of kiln you want to build? Have you checked out your local fire ordinances? I’ve heard of too many kilns having to be torn down because of complaints by the neighbors or passersby. Giving a few mugs during an information session to the local powers that be can eliminate problems before they start. Finally, can you afford it?
That’s my manifesto on how we fire the UW-L kiln. These instructions must be taken as general theory. One definition of woodfire is: surprise! This works for our undergrad program and makes a lazy way for me to fire and continue my search for subtle colors in brown. Someday I will thank the person who told me not to attend the Woodfire Conference in ’91.