Building a Kiln (Part 2)

My new combination wood/propane kiln required about 500 bricks to build. The inside shell, because it will be exposed to the flames and wood ash, is made entirely out of Bruce Bartol’s high duty fire brick with an outside shell of insulation brick that I reused from previous kilns.  The plan for this kiln did not call for mortar between the joints so getting a good tight fit between bricks was important and required grinding off anything that wasn’t native to the bricks when they were made.  Cleaning bricks, thanks to an angle grinder and about fifty abrasive discs, took about two months of working a few hours each day. Bruce mortared the bricks together using a mixture that was mostly clay, which thankfully didn’t take a lot to remove. The amount of dust generated, however, was impressive and so I worked outside and with temperature sometimes below zero, I chose my work hours carefully.   Bundled up in multiple layers of clothes, my nose and mouth inside a respirator, ears and eyes under their respective protection didn’t allow a lot of mobility, but enough to get the grinder on the old remnants of mortar and the accumulation of salt glaze.

The kiln’s design is unique in that there are two flues built into the bottom of the kiln. Each of the burners is matched up with one of the flues which allows the flame to travel under the pots stacked above, up the inside the kiln to the bottom of the arched roof before the flame gets drawn back down to the bottom of the kiln where it exits into the chimney flues that runs down the middle of the kiln floor. The kiln’s design is also complicated because of the need for two fire boxes, one on each side of the kiln’s main chamber, and a door for each for stoking the fire with wood.

There were two things that I really like about building a kiln that can be fired with propane or wood. The first is because of all the things- expected and unexpected- that can happen when firing a kiln with wood and the complex process required to achieve good results. The second is because I own land that is mostly covered by trees that I work with a consulting forester to manage in a sustainable manner. I have a lot of potential fuel.

The deposits of wood ash that settle on pots on their way through a kiln melt when the temperature reach about 2300. The melted ash forms a very unique glaze that varies with every firing. The flames, intense heat and ash leave behind flashes and streaks on pots it comes in contact with and the results are different colors and tones that range from a mottled green to red to dark brown.  I was eager to fire the new kiln and looked forward to the long hours of cutting wood, drying it, getting it ready for stoking and feeding the stacks of wood into the fire boxes that would be necessary to get the kiln up to temperature. I would invite friends, both potters and non-potters to firings, share food and drinks in the studio and listen to music.  I flashed back to RIT and the camaraderie that developed among those of us who volunteered to stay up all night, feeding wood into the kiln, monitoring the kiln’s puffing and coughing during stoking, then watching with a fair amount of awe and fear as the wood took off, the roar of fire and flames shooting out of every opening between bricks and spyholes and then repeating the cycle over and over, again and again. I wanted to experience all of this, forty-five years later.  

I also wanted to fire a kiln with wood because it felt like a more responsible thing to do instead of relying on a finite supply of fossil fuel like propane. My studio is surrounded by woods. After I retired, I bought a portable sawmill and in addition to being able to turn some of the trees into lumber, it provides an abundance of wood slabs that are a byproduct of sawing. In thinking about firing a kiln with wood, it was mostly the slabs that I anticipated using for fuel. The plan made sense for many reasons and just felt right.

              

I finished building the kiln in about a year and a half.  I decided that for the first few firings,I would fire the kiln with propane in order to work the bugs out and get to know the kiln. The first firing would be a bisque (pots without glaze) firing consisting entirely of recent work.  Having pots go through a bisque firing at about 1800 degrees prepares them for the higher temperatures of a glaze fire of 2300 degrees. Loading the kiln for a bisque firing is also much easier than loading a glaze kiln because pots can touch as temperature are not high enough to fully vitrify the silica in the clay. The first firing of any kiln is a challenge, especially for me given it had been a few years since I had fired a gas kiln, let alone one that was untested and new. I was hoping for some good karma channeled from Bruce Bartol and his old salt glaze kiln bricks

There’s a lot that can go wrong when firing a kiln, especially a new kiln. It can fire too fast and hot, have the wrong balance of gas and air, the chimney may not draw well, the damper may be ineffective or the kiln might not heat up sufficiently to reach the maximum firing temperature. Most of these problems can be averted when designing a kiln or remedied during later firings by making some adjustments inside the kiln. The last problem of not getting up to temperature, which typically is caused by undersized source of heat trying to heat up a volume that’s too large, is more difficult to solve. The solution is either bigger burners or a smaller kiln.

I loaded the kiln for the first firing and once the door was closed, except for a small opening at the top of the door that allowed the last remnants of moisture to escape during the first few hours of firing, the kiln was ready. I lit one of the burners and then the other after an hour. To have an accurate reading of the temperature inside the kiln during a firing, I use a pyrometer, which is really a fancy thermometer that can withstand the very high temperatures of a kiln.  As I monitored the firing during the first few hours, the temperature seemed to be climbing, but slowly. Even though the temperature when I lit the burners was only a few degrees warmer than the air temperature of 10 degrees, it should have increased quite rapidly once the burners were started.  Getting up to 1000 degrees took almost five hours and with 700 more to go, I was getting anxious especially given that I was hoping to finish firing in six hours. The kiln effectively stopped increasing in temperature after seven hours and clearly was not going to reach the goal I had set. After thinking over my options for an hour and watching the pyrometer reading remain constant, I shut the burners off, closed the damper and called it a night.  On the walk back to the house, I ran a few questions over in my mind. Had the kiln fired the pieces sufficiently to reach at least the low end of a bisque temperature of about 1500 degrees? If I was not able to reach 1700 degrees, what was I going to do to get the kiln up to 2300 degrees for a glaze firing? Was there something wrong with the kiln that was correctable or had I undersized the burners or oversized the kiln or both?

A little time away from any challenge can offer fresh perspective and so not thinking about the problem with my kiln for a couple of days was good. A few days following the failed firing, I walked out to the studio and looked at the kiln thinking that an answer might be evident if I looked at it long and hard enough. As I eliminated possible causes that could be at the root of the problem, I kept coming back to the same conclusion- the burner capacity was too low or the size of the kiln was too large or both.

The burners were definitely on the low side of acceptable rated at 250,000 BTU/hr. each for a kiln made completely of hard brick and its size. I knew that when I designed the kiln, but thought with a little longer firing schedule, the kiln would get up to temperature. Buying two new burners that would have greater output could cost as much as $2,500. I could probably sell my old burners for half of what I paid for them, but still a lot of money in order to stick to my out-of-pocket financing and business model. I could reduce the size of the kiln by taking the kiln down and rebuilding a smaller version. I had a studio full of pots and glazes ready to apply but didn’t have a functioning kiln to fire.

Just before placing an order for two, new, larger burners, I paused and started wondering if that was what I really wanted to do. A friend once shared with me that when you’re sailing and find the wind has pushed you way off course, the goal isn’t to get back on course, it’s to look toward your destination and figure out the best way to get there. While building this kiln was the course I had charted, my actual destination was to integrate being a potter into the life I had created during the forty-five years since leaving it.  I started to think that getting back on my initial course wasn’t going to help me reach my destination.

One thing I kept thinking about was how different my life is today compared to 1970 when I was in college. I guess it goes without saying, but back then I had just a few things to think about.  My parents supported me through college so I was able to spend all of my time focused on school and ceramics. Even over the summer, my focus was making pottery to sell (the word “sell” should really be in quotes, because there wasn’t a lot of that) at fairs and shops and my parents supported me in doing that. Now, looking back, I realize their support and my singular focus on clay was not necessarily a good thing. I didn’t have to make sure the income and expenses balanced out and I had few responsibilities to assume other than pottery. That’s all changed during the forty-five years between then and now. 

I was also struck, as I reflected on the past few months devoted to making pottery, how much more difficult it is now to make time to put my full attention into my work. I know that it’s all about the choices we make, but when I was in college, there weren’t as many choices about what to do with my time because the layers of my life were just starting to be laid down.  Could I give up some of the responsibilities that I have today, peel off a few layers and find more time to devote to pottery? Sure! Do I really want to? I’m not so sure. So what I started thinking about as I looked at this beautiful kiln I had just constructed over the past two years with bricks from an old salt kiln in Maryland and that now needed some tweaks to make it work was how could I integrate my new venture of returning to making pottery into the life that I’ve created and love? Back when I was 18, I worked hard to build a life around pottery, now I was trying to make pottery a part of a life already built.

Two days later, my son, Jackson, came over to the studio and in two hours the kiln’s arc was down and the next day the entire kiln was piled up on the floor. Two days later a young potter, Travis, from a community not far from mine answered my advertisement on Craigslist and made his first of three trips to pick up the 500 Bartol bricks I used to build the wood/gas kiln. Travis graduated from college in Oregon after serving a few tours of duty in Afghanistan and it was his dream to build a wood fired kiln once he gets settled in at his own place. He shared with me that firing a wood kiln was the most amazing experience he had in art school and he couldn’t wait to pick up where he left off. Knowing this dissolved most of the feelings of failure that I had about not realizing my own dream of building and firing a wood kiln. It also helped that I have a pretty good pile of Bartol bricks still in a pile that I’m hanging on to for now because you never know. Luckily, all those piles of bricks from Maryland turned out to be a lot more than 500. Bruce Bartol and his bricks live to see another day.  

Now, I’ve got to get busy and build a new kiln.