WAYWO: Kilns

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This week ol’ Marko is here to share his callouses and minor burns and a bunch of photos from this summer involving one of my passions: pottery.

I’ve been a part-time potter since high school. I helped build a few kilns in the summers with my fellow potters around Dane County, Wisconsin over a quarter century ago and my first job after moving to Europe to live in Prague was teaching ceramics to children. The photo that opens this diary is from the second to last firing of the old, wood-burning kiln that I built behind the barn on a little bit of heaven owned by my Czech family. The chimney on the old kiln was not terribly stable or durable and after a very hot firing, which managed to reach temperatures just over 1200 degrees Celsius, it developed so many cracks that the next good gust of wind blew it over. This year I finally tore out the foundation of the chimney and after gazing at the demolition zone I decided to try to rebuild the whole kiln, make it slightly larger and more efficient. I thought I’d try yet another experiment and do something that I’d never seen done before.

Your basic kiln which is fueled by wood has three main sections: a firebox where you light a fire and feed it lots of wood, which sends flames into a chamber containing all the dry clay objects you wish to have fired, the flames are drawn through the chamber by a chimney. In primitive kilns these three parts are reduced to a simple pit in the ground which is covered with a dome of clay and perhaps rocks with a hole in the side and a hole in the top.

On a recent trip to Tuscany I visited an Etruscan necropolis where there were also exhibits set up to show how pottery was made during the Iron Age.

Some primitive kilns used during workshops at the archaeological park.

Firing clay is a process of using heat to change the chemical structure of the clay itself. Once clay reaches a certain temperature all the water that is chemically bonded within the material is burned off and it ceases to be clay. The physical structure of clay is microscopic platelets. When they get wet the water causes the platelets to adhere to each other and together they form a pliable material, strong and water resistant like the flat shingles on a roof. During firing the platelet shape itself is lost and no amount of water added to fired clay will ever allow it to regain its pliability. Potters basically make artificial rocks.

There are two main stages to firing. The first stage ends at the bisque state, generally around 880 degrees Celsius (yes, that’s hotter than a kitchen oven and you could bake a clay pot in an oven for centuries and it would never be fired. It’s the temperature that’s important and not the time). Reach that temp with your clay and congratulations! you’ve made a rock. The final temperature of the second stage is more variable. It’s the temperature where the clay begins to actually vitrify, to melt. There’s a temperature range of hundreds of degrees between the red terra cottas and the stoneware and porcelains.

Um, can you tell I used to teach this stuff? Sheesh, but I do go on and on, don’t I?

Anyway, back to my project--

In my old kiln I had to build a new wall to the firing chamber every time I fired the kiln. I’d load the kiln with my creations and the creations of my friends and then have to build a wall to close off the chamber. And after firing I’d have to tear the wall down to get everything out of the kiln. Not ideal. I found a smaller door for the firebox and moved the frame of the larger door up to the chamber. I would now be able to just lean through the doorway and load and unload.

We invited some friends over to participate in the firing. One friend, who provided most of what was actually fired, attends my little kiln firing parties regularly. I’ll show you some of his work in a bit (or you can hop over to his Instagram page and see a photo of him and me posing in front of the kiln— me in my hipsterific ironical T-shirt bought for a single dollar in adorable Hurley, Wisconsin). He and my sons showed up to the party a few days early to help me get the guest of honor ready. There was so much clay to be mixed with sand and sawdust and applied, there was mortar to be mixed and bricks for the chimney to be laid…

Finally, around 4:00 in the afternoon, we were ready to load the kiln. There were parts of the kiln that still needed some work, the chimney wasn’t quite finished, some of the edges could use another layer of insulation, but I’d agreed with my friend that we were just going to aim for a bisque firing this time around. Everything was still so wet, it would have been crazy to try to get it up over 1000 degrees. I lit a few candles in the firing chamber to help warm things up slowly.

I decided to help insulate the door to the chamber by building a wall inside the kiln and while constructing it from loose bricks I managed to drop one into the chamber. Idiot! I completely ruined one of my friend’s beautiful sculptures and a pot someone else had made. Another piece of my friend’s was sorely wounded and I removed it from the kiln to be repaired at a later date.

A few guests arrived and a couple last minute little figures were blobbed together by kids and their parents. I tucked them into corners of the firing chamber and rebuilt my ill-fated wall, covered it with a sheet of scrap metal and a blanket of ceramic wool.

I started a small fire in the firebox around 6:00.

There was eating and drinking and merriment.

Around midnight the first flames were visible coming out of the chimney.

I didn’t have a great deal of time to take pictures. Nobody was particularly eager to replace me in my position as official stoker of the flames. I kept the fire very small for a couple of hours. Then a medium fire for an hour or so until, around 9:00 I think, a pyrometric cone set to melt around 650 degrees drooped over and I began to pile the wood on.

The firing continued well into the night.

And around two in the morning the second pyrometric cone drooped over when we managed to pass the 850 degree mark. I kept things going for another hour or so. The cone for 1043 degrees was still standing when I stopped feeding the fire and blocked up the air-intake holes and capped the chimney.

When I left a day later the kiln was still sealed.

This last weekend I set up a second kiln.

A raku kiln is easy to set up and firing each piece takes less than an hour.

So, that’s my big creative project for the Summer. Slowly getting back into my graphic design work and comics. I should also make a few pieces to go into the kiln in the Spring.

What are you working on?