Here are some of the things that will go into the Feb. firing. Small plates that will be about 12cm fired, and some larger plates about 24cm fired. Clay body is Karatsu white from Hara san and Kishidake clay 50/50, with pulverized sandstone and weathered Shirakawa porcelain stone wedged in.
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.
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.
Well, usually at least. This last couple of days was an exception. I started dabbling in some nifty new technology (to me). This involved casting some new tools, so when the old ones wear out I’ll have some ready to go. This tool is called a Gyubera, or cow’s tongue rib, that is sort of indispensable when making a lot of Karatsu forms.
The problem with them is that it is awfully hard to find them in the right shape for what you need. There are a lot of cheap ones on the market which are, well, cheap. The one thing they have going for them is that they have a lot of extra wood on them so you can do a lot of fine tuning with a rasp and sandpaper. The good ones are good, but cost a small fortune. I paid about $80 for my large one that I use for teabowls. Smaller one was about $50. Am I the only one that thinks that is ridiculous? Well, they were handmade one by one, by a barber. As strange as that sounds, there was this one barber that made really nice gyubera. He is now retired, and though someone took over his business, the new guy needs practice.
However, the big problem with all the aforementioned gyubera is that they are made of wood and prone to cracking and rot. It’s kind of a ‘heads I win, tails you lose’ situation. If you keep them damp, they rot. If you let them dry out, get wet, dry, wet, repeatedly, they crack. I found a partial solution to this by soaking them in Minwax wood hardener, and applying a layer of epoxy. But the epoxy bubbles up with time and they wood hardener wasn’t enough to prevent cracking over the long run, although it did extend the life of the tool considerably.
Not wanting to have to buy more, because of the cost and the fact that the new guy still needs practice. I thought I’d just make some myself, but it didn’t solve the wood material problems. So, these last couple of days I spent making plaster molds of the original gyubera, and using dental grade acrylic resin to cast new ones. I got the resin from a friend who used to be in the business. It is a funny pink color because it is supposed to look like gums. Aesthetically speaking, not my favorite for clay tools, but on the bright side it is unlikely I’ll ever get my tools confused with someone else’s tools.
After a couple of tries, I got a pretty good working two piece mold of two gyubera side by side. Got it ready for the resin pour and got the resin poured without too much fuss. Once it was poured and set for about 20 minutes, it was ready to heat cure in a 50C hot water bath for 25 minutes. Strangely, all of this went fairly smoothly. The problem came with trying to get that mold apart later. I tried and tried but it was not happening, and I ended up breaking the mold. Still, the casts were covered in plaster, because the liquid of the resin had penetrated through the release agent into the plaster. Oops, guess I should have used the special acrylic resin release agent instead of the casting slip release agent. Live and learn.
The cleaned up casts will make usable tools, but they are pocked with bubbles and other spaces where the resin didn’t flow properly. I’ll have to try again, improve the craftsmanship.