Took a hike up the mountain today to the now closed Shirakawa Toseki (porcelain stone) mine. This was the base ingredient for Arita’s glazes for hundreds of years. The mine is extensive, but I stayed near the entrance as old mines are not among the safest places on this earth. The passages from the main entrance radiated out in several directions and where light still filtered in, you could see that some of them extended several hundred meters. And that is just what you could see from the light filtering in. Who knows how much farther they go?
In the entrance area, pillars of rock were left to hold up the roof, but there were boulders in several places on the floor, from what looked like recent rock falls. The roof of the cave is probably about 20 feet tall. The expanse of white rock is really stunning to see.
The last firing of the wood kiln, I mixed up a glaze of 65 mystery wood ash and 35 Amakusa porcelain stone. I expected a dark green or yellow glassy ash glaze that didn’t run much. I even had the test tiles from around 5 years ago that showed what I’d get.
Well, I ended up getting a rust red sintered crust on every pot I put that glaze on, and it was a lot of pots. Even in areas that got up to cone 13, that glaze did not melt. It was very confusing since I had the test tiles showing a green glossy glaze.
With the new tiny kiln, I was able to fire twice today, 2 sets of test tiles. One set using the mystery wood ash from the crusty rust refractory debacle, and the other set using my normal mixed wood ash. Each set was fired for 90 minutes to cone 9 (yep, just 90 minutes to cone 9!) and all the recipes were exactly the same save for the type of ash.
I think it is safe to say that these ashes are not interchangeable. The mystery ash was from a neighbor’s wood stove, and I have no idea what it was. At any rate, it seems to have been reduced to almost pure silica. Sure enough, the glazes with the regular mixed wood ash turned out as expected. The atmosphere in the tiny test kiln is interesting. The 80/40 test tile came out reduced while the others were oxidized, only 2-3cm apart in either direction.
So, in short, mystery solved, and it didn’t require waiting for a big kiln firing. All in all, this tiny kiln is turning out to be very useful indeed, and easy to fire.
My weed burner came in the mail this afternoon and I wasted no time getting everything ready for the first real test of the tiny test kiln.
I prepared 3 sets of glaze tile pairs and set them in the kiln, along with one Orton cone (#6). I fired it up at 4pm. At 5pm cone 6 was flat. Easy peasy! Next time, all the way to cone 10, when I have some more free time for testing.
Karatsu potter Okamoto Sakurei just ended a show in Fukuoka this weekend at Gallery Ichibankan. For those of you who haven’t heard of him, Okamoto san is a very talented artist making Karatsu style wares. He is well known throughout the country and one of the top Karatsu ceramic artists today. He will also be doing a demonstration/lecture for the Workshop in Taku 2012: The Simple Teabowl.
During my visit we had a chance to discuss his upcoming presentation, as well as some wood firing diagnostics. Here are some of the pictures from the show. The gallery used a lot of natural light from its windows, which made for a very nice display, however it was not so camera friendly.
Since switching over to the new wood kiln, there has been a need to tweek my gas kiln glazes, as well as develop new glazes for wood firing. Problem is, it is hard to test new glazes because the wood kiln gets fired infrequently, and I fire the gas kiln much less now because most of the work goes into the wood kiln. So I need something that I can fire test tiles in, and after looking at some little electric test kilns, (and their prices) I decided to build a propane gas fueled test kiln.
I had the materials laying around, and scavenged some from previous projects. I came up with this little Itte-Koi (going and coming) style kiln. It is basically just a scaled down version of the first gas kiln I built 7 years ago. This one only required about 20 bricks, and the hardest part was carving the chimney bricks. Thin brick slices hold up the floor/shelf, the flame goes in the bottom front, climbs up the rear and comes back around down to the exit flue at the middle front.
The chimney brick shown strapped to the front was a mistake, I replaced it later with one that wasn’t cut through completely. I had carved this one through because my larger version had a passive damper here, but it seemed like too much trouble on this tiny kiln. Much easier to lay a slice of brick over the top of the chimney.
3 more bricks across the top finish the kiln. I later set the whole thing on a flat stand with wheels and fired it up with a raku burner I had laying around. Waaaaayyyy overpowered. Within 10 minutes I had red heat in the chamber, but there was a tall flame coming from the chimney because of all the unburnt gas igniting as it left the kiln. This with the regulator set about as low as it would go, so I need a smaller burner, probably a small weed burner or reduction burner for an electric kiln would be about right. I’ll post on this kiln again once I get a burner to fire it with and some glaze tests set to go!
Spend a good bit of time sorting and splitting wood for the next couple of firings today. Before the kiln was built, Craig Edwards mentioned on a couple of occasions that having the wood split and sorted makes for a much easier time firing. I understood the need for splitting, but sorting kind of stumped me. I couldn’t understand why sorting for length would help, thinking that one could estimate the volume of wood going in each stoke, more shorter pieces or less longer pieces, right?
This seems to work in theory, but when you start adding in factors like stoking under the grates vs over the grates, or doing the wooden door technique, or side stoking through a smaller hole that tilts down, then the size and length of the faggots gets pretty important pretty fast. Having to sort through a stack for the right size during the firing makes for a stressful time. Having the right size stacked in the right place so that it doesn’t need to be moved a lot really cuts down on the labor.
So, this time I culled out all of the longest wood and split it first, stacking it near the front of the kiln. Shorter fat pieces near the front as well, with thinner pieces toward the middle and rear for side stoking the front and rear chambers. Also a special section of extra long pieces for doing a wooden door type stoke to get over stalls, if they happen. Here are some pictures of the stacks, plus a little potter porn.