The Wood Firing

Hi Guys!

I fired my small wood kiln. I will try to share the whole process with you!

 A kiln is a type of oven that ceramicists use to cook pots to a high temperature so they become hard like stone. The kiln I am using is a small variation an an anagama kiln called an Ittekoi kiln. An anagama kiln is a Japanese kiln that uses wood to raise the temperature of the kiln chamber. Anagama kilns actually came from China around the 5th century, but now are seen as traditionally Japanese. Traditional Anagama kilns can be small, like the one I am going to use, or as large as the side of a mountain. Here are some pictures of a traditional kiln  in the town where I am staying, Shigaraki, that dates back to the very early 20th century. As you can see, the kiln has many openings, or chambers, where hundreds of pieces of work would have been loaded and fired.

This is the front loading opening of a large anagama kiln we have in the Sculpture park. As you can see, the kiln is built into the side of the mountain, with its many chambers covered by dirt.

 

Here is a diagram of what the kiln looks like on the inside.

 The chambers climb up the side of the hill in steps. The artists start the fire in the first front chamber. As the chambers reach temperature they are closed up and the artists begin firing and stoking the fire in the next chamber. They continue this process until all of the chambers are at the correct temperature. This can take days or even a week, depending on the size of the kiln.  They then have to wait for the kiln to cool which can take 2 weeks or even more. 

Here is the Ittekoi  kiln I plan to use.

As you can see, it is much smaller than a regular anagama and it is built above ground. This kiln will only take 12 hours to fire, and a couple days to cool.

  Wood kilns are now used all over the world by ceramicists to create interesting surfaces on their pieces.  The ash from the burning wood settles on the pieces and creates a glaze on the pots. The longer the kiln is fired and the ash allowed to settle, the more glaze you get on the pots. The flames and the heat from the burning wood can also cause "flashes", bright spots of color, usually orange or red, to form on the pots. In the town of Shigaraki, Japan, where I am staying, they even have a special clay that is used in wood firings. The clay is mined in the mountains around Shigaraki and contains a lot of iron, grog (pieces of stone and sand), and feldspar (pieces of silica or glass that melts and forms white nubs on the surface of the clay). Because of the large amount of iron, this clay flashes very well, and you get large red and orange spots on the pots.

 This is a bowl by Shigaraki artist Kato Hajimu. You can see the orange flashing and the feldspar spots.

Now to start the process! The first thing you need to do is chop wood for fuel. Each kiln takes a different amount of wood. This is the amount I need.I know it is a lot! And I didn't just chop the wood. I got to use a chain saw!!

Next, you collect the wood in easily accessible bundles and carts.

Then you have to make sure you have all of your pieces ready!
Here are mine. Some are glazed and some are not. I fired the kiln to 1,230 degrees Centigrade (2,246 degrees Fahrenheit).

I then prepared the kiln. You have to add shelves to the kiln so the work has something to sit on.This is a picture of the stilts that will hold the shelves.

I then used this special clay to keep the pieces from sticking to the kiln shelves. If you do not use this clay, the melted ash will make the pieces stick to the kiln!

Then you load the kiln! I forgot to take a picture of my loaded kiln! here is a very dark shot while we were closing the door.

And here is a picture of my friend's loaded wood kiln, just so you can get the idea of what it looks like.

Then you need to close the door. This can take a lot of time because in most wood firings at the park there is no set way to close the door. You have to find the right configuration of bricks to create the most amount of coverage for the opening. Once you have the bricks in place you have to use the special clay again to block up holes and cracks. This allows the heat to stay in the kiln and not escape through the spaces between the bricks. You also have to leave room for the thermocupplers. These are large instruments that measure the temperature in the kiln. One is placed on the top and the other on the bottom. Then wires form the termocupplers are attached to a digital reader that tells us the temperature.You can see the wires in the pictures below. These instruments will help us keep temperature on track while firing the kiln.

The Digital Temperature Gage

This is the firing plan for the kiln. The line shows me  the temperature the kiln should be at every hour. We try to stay as close to this line as possible. But sometimes that is very difficult.

As you can see, this firing went way off schedule. The temperature rose too fast and at some points would not rise. But the results turned out fine regardless.

I also createsd a small kiln spirit to guard the kiln and make sure everything turns out okay.  I gave mine big eyes so he can see any problems. I named him Bob. I hope he does a good job. YAY BOB!

After everything is prepared, we must make the fire box next to the front opening of the kin.  This is a stone chute that more easily allows stoking of the kiln.

Finally we can start firing! To start the firing you put split logs of wood into the kiln opening. You then create something similar to a campfire in the firebox. Adding some small kindling to larger sticks and logs to create a roaring fire.

Here is a video of the warm up. 

Over the next 12 hours the fire must be continually stoked to raise the temperature.  Logs that are wet take longer to burn and therefore must be left to dry before being put in the fire. 

 

Eventually a roaring fire begins to form. The fire raises the temperature in the kiln until the clay hardens and the ash melts

Here is a video of the fire!

Once the temperature is reached, it must be held for an hour or more to ensure the melting of the ash and flashing of the fire. Then the kiln is closed up to stop the heat from escaping. The fire will burn out and the kiln will slowly lower in temperature until it is cool enough to open and unload.

Here are a couple of pictures of how we closed up all of the openings, so the heat would not escape. We use bricks and clay to tightly seal all of the cracks and holes.

It took about 36 hours for the kiln to cool enough for me to open it. I began to un-brick the door and this is what I saw!

 The firing went really well! I got a large amount of orange flashing colors, as well as some shine and color from the ash. 

 Before I could take beautiful pictures of these new pieces, I needed to clean up the kiln. All of the shelves, stilts and bricks needed to be cleaned and ground down so pieces wouldn't stick to them in future firing.  The ash also needed to be swept out of the bottom of the kiln.

 It is hard work, but if you make sure you clean up well every time,  the next firing will go much more easily.

This firing went very well! I got some beautiful pieces and I can't wait to fire again. I hope you enjoyed the process. Here are some pictures of the final pieces!