Category Archives: kiln

Firing for anyone

In Japan, people often visit pottery studios for a short pottery experience, either painting something or making something small to be glazed and fired later by the studio owner or a craftsman. This has always seemed so limited to me, and the inevitable comment, “Oh, you are so lucky, I wish I could do this every day!” always prompts my response: “Yes, me too!”. Most people just don’t have any idea what goes into a finished pot. Turning it on the wheel is maybe 10% of the overall process, much less if you gather materials yourself and/or wood fire  your work. And customers rarely see the failures, or all the polishing that goes into a piece and assume the potter just opens  the kiln door to a batch of warm, super looking, ready to sell pots.

Finding a way for people to experience more of pottery making is a challenge, because of the time it takes drying, bisqueing, firing, and waiting to cool down. Raku firing abbreviates this a lot, but still requires a lot of specialized equipment in most cases. Shichirin fired pottery, for me, is a good way for anyone to have a firing experience, including the excitement of the fire, the engagement with the work, the post fire polishing and critiquing, and even the failures and serendipitous successes.

Lately I’ve been working on a firing method that is accessible to everyone, with items available at most home centers. I got this idea years ago when a Japanese potter named Yoshida (don’t remember his first name) made a splash by introducing “Shichirin Togei”, which used a  small Japanese BBQ, called a shichirin, to fire small objects. This developed into a book called Minigama, which I never read, but outlines the construction of small handbuilt kilns from fireclay and fired with wood, charcoal, and forced air. I think the book is out of print now.

I liked the idea of shichirin togei, but thought the open shichirin was maybe not so efficient at getting up to temp, so I added another one on top, like a clamshell, with both shichirin wadded together with a coil of clay. The bottom damper is the air port, and the top damper is the chimney opening and stoke hole.

You start by packing some charcoal into the bottom of the chamber, around a stilt on which the pot will sit. Then place the pot on the stilt and continue covering with charcoal. Then place a coil of soft clay around the mouth of the shichirin, and overturn the second shichirin over it.

Now that that is done, time for the fun to start! Use a hand torch to light charcoal, then use a hair dryer to get things burning hot.

Now just wait for things to heat up, it will take a few minutes, after which flames will start to emerge from the top damper hole.

This flame should continue to grow and get jumpy, making noise as unburnt gases from inside the chamber exit and combust when they meet more oxygen.  Keep slowly adding pieces of charcoal from the top stoke hole (damper), keep that flame extended. As it gets nice and hot, you’ll be able to tell how the kiln breathes every time you put in a piece of charcoal, and you’ll get a sense of when to stoke.

The first firing might take about 45 minutes, because of the time to heat everything up. From the second firing, 30 minutes seems to be enough to fire the clay. If you have time, you can go longer, and ash from the charcoal will leave more green ‘glaze’ on the surface of the pot.

I have this recurring nightmare…

before every firing of the wood kiln. Actually it is four separate recurring nightmares. In the first, I am loading pots onto normal wood shelves in a fairly standard living room, for some reason not worrying that the lot of it will burn up with the entire house. BUT, for some reason, I always remove all of the lamps and light fixtures, because they and they alone can’t handle the  high temps.

In the second, we are firing the kiln as usual, and we are into the third day, just hours before finishing and I realize that I FORGOT TO LOAD THE KILN… This one is by far the worst of the dreams. The feeling of sudden panic is positively sublime. Very happy to wake up (and realize it was just a dream) after this one…

The next is not quite as bad as the previous, but still pretty unsettling.  It starts out well enough: I have just unloaded a very successful firing and am so happy with it that I decide to fire again. Because it is a dream, I miraculously have enough glazed ware to load the kiln up again in about 2 days (Normally takes me 10). I get everything loaded, and start the fire, but about a day into the firing I realize I ONLY HAVE ONE DAY WORTH OF FIREWOOD! This one also wakes me up with that icky panicky feeling.

The third is not a nightmare per se, but a recurring dream about a kiln that doesn’t exist. It is a large single chamber, with white interior, and there are shelves on the walls and in the center of the large chamber on a sort of island. The floor, walls, and island are all white and rough with kiln wash. There is no chimney, and the kiln is connected to the fire box via an elevated brick tunnel, which goes out the rear of the chamber about 2 meters, turns 90 degrees right, stretches about 8 meters, then takes another 90 degree right turn, where extends forward and turns into the firebox. From the firebox to the kiln forms a large U shape. Even more strange, the firebox is open to the sky and steps up to the flue channel, which somehow ‘sucks’ in the heat of the fire. The firebox is probably 4 meters long/deep, and the wood used is huge: entire tree trunks shoved in and stacked in a criss cross pattern, burning.  Any one have a kiln that looks like this?

Coming up to this fall firing in Oct., I feel as though everything is under control, and no particularly strong feelings of anxiety, yet the dreams continue, including 2 nights in a row now, a dream of some of my teeth falling out. Seems quite normal in the dream at least…

Bummer…

This just made me sad when I saw it this morning. We had a LOT of rain over ten last 36 hours, and I think the footers sank a bit, tilting the stack forward, then dumping it. This will take some time to clean up.

** Just one quick amendment to this post: on re-reading the post and comments, I realized that I may have mislead people to believe that the stack (chimney) went over. Not so, thankfully. Just the stack of wood. No damage to the kiln other than a few scratches to the insulating top coat, and about 5 unlucky shelves that had been sitting right where the wood struck.


-Posted from iMike

Location:Taku, Saga, Japan

Shell geekery for shell geeks

Warning! Geek alert!

Today on the way back from teaching, I stopped by the seaside shell pile to collect some cockle shells for firing. Though I usually don’t find “the good ones”, today I got lucky. Pictured below are the two types in the area. The thin type with the many, shallow grooves comprises about 99% of what one can find, so I usually use those, but today I found quite a few of the deeply grooved bumpy, thick shells. These are better for standing pots on because they are thicker and don’t collapse in the firing, so they don’t need to be stuffed with fire clay, at least for small to medium sized items. They also leave a more interesting mark on the pot.

“Hi, I’m Mike and I’m a shell wadding geek.”

“Hi Mike” (SWG Anonymous group murmurs)

Gas kiln with saggars

People sometimes lament the limited effects possible in gas and electric kilns compared to wood kilns, but there are ways to get many interesting effects in gas and electric if you use your imagination and do some experimentation.

This time around I loaded about half of the kiln with saggared ware. 4 incense burners, 3 sake cup refires, 2 boxes, 2 teabowls, and 1 frog toilet (in porcelain, no less).

The incense burners came out most interesting, with a lot of deformation occurring in the clay, which was the goal. Nakayama kun wanted some burner bodies that were deformed and all around ‘grungy’ to fit with silver lids. They were wrapped in rice straw rope that had been soaked in a saturated solution of soda ash, mixed with some feldspar, the idea being to get some focused area effects on the pot surfaces. The soda ate into the clay in places and fluxed the feldspar nicely. One of the burners completely collapsed and stuck to the saggar and the adjacent burner, but I’ll be able to keep 2 out of the 3.

Two of the teabowls, with iron based glazes turned out nicely, but one (the black one) stuck to the saggar and will need some repair on the lip. Nakayama kun is going to do a silver repair on the lip, and I’ll post a picture when it is done. The other, and iron saturate glazed bowl, turned out nicely but I really can’t decide if I like the glaze color or not. Need to whip up some tea in it to see if it shows off the tea color well or not.

The porcelain ring boxes were a complete failure, with cooling fractures I think. I drizzled in a soda/spar slurry on the insides and it was waaay too thick. I think its expansion and/or contraction fractured the pots.