Lately I’ve been experimenting with ways to age pots more quickly, making the crackle stand out. This time I tried an old woodworking trick, and it seems to work nicely.
I soaked the pots in a strong tea bath then dried completely. After that, I applied iron acetate with a brush and let them sit a couple of days. The iron acetate reacts with tannins and turns a dark color within about 3 days. I made the iron acetate by soaking steel wool in vinegar. I may change to a weak sulfuric acid solution, since the smell of the vinegar is proving difficult to get out of the pots!
I finally sat down and figured out how to use my video camera and software. For anyone who is interested, here are some videos I posted to youtube.
All of these pots were made with clay from the property, discovered right under where we built the kiln. It has a lot of iron, but still takes some heat, and won’t bloat at higher temps. Probably due in part to the fact that it is very open with a lot of sand and other even larger inclusions. Even vitrified, it still sweats because of the openness. With use, the sweating stops, as all the pores fill with minerals from the water and tea tannins, etc…
This post is a photo record with comments, in order to organize and retain my thoughts and observations about the 8th firing of the wood kiln. I always think I’ll remember until the next firing, but never do. So, if you get into this, beware there are a LOT of pictures, some of which may seem redundant. There are examples of most of the pots from the firing, minus teabowls and some others which are not photographed yet.
The 8th firing was a charm overall, with many good pots, some bad, and some that will get refired. Kiln was fired in oxidation primarily. We stoked once every 30 minutes for 2 1/2 days, then once every 20 minutes the last half day.
– Front was nicely melted, nice even gradient to the rear of first chamber, E-Karatsu was about ideal. Cone 12 at hottest front down to cone 6 at coolest rear.
– Front chamber behaves like anagama. No significant temp gradient from front to back of each setting. Next firing, will pack kiln by eliminating the space between settings, leaving horizontal space for flame travel. One long setting from front to back of first chamber.
– Ame yu better at low temps. Load rear to mid chamber.
– Ao yu needs more heat, mid to front chamber.
– Large platters go midway to back of front chamber. Too much ash up front.
– Firebox wares are very nice in a three day firing. Great place for Shino, under cover to avoid ash in pots.
– Rear chamber fires fast when preheated for 3 days. Jumped from 1044C to 1344C in four stokes, a little over an hour. Care must be taken to spend more time soaking at high temp, because rear chamber high temp wares not quite mature (surface changes only), clay not melted well. Spend 3 or 4 hours firing off rear chamber, slowly, to get inside the pots.
– Rear chamber fires very evenly front to back, and top to bottom. Pick a temp to fire at and load accordingly. Don’t expect a significant gradient.
Here are the first of a bunch of water jars and flower vases that are going into the kiln this early fall. I really needed some practice coiling, paddling, and collaring in necks on the kickwheel and 船徳利 funadokkuri (boat flasks) are the perfect shape for it. Traditionally these were used as flasks for oil, etc. on boats. They needed to be hard to tip over, hence the wide flat bottom. Now they are mostly used for flower arrangements.
All of the water jars will have wooden lids made for them. I’ve done one or two in the past with surprising positive response from viewers/customers. The lids are fun to make, since they are a non traditional item, you can play around a bit with them. I’ll post some lids later on, if the pots make it through the firing.
Well, time to sit down with the last firing and figure out what went wrong, and what went right.
Firing and packing: Great. With this firing I figured out, FINALLY, the proper exit flue volume to use. And with it, the proper packing procedure. The kiln climbed steadily, without effort, for 45 hours and the flame in the front chamber reached front to back really nicely. It turned out to be a fairly even gradient from front to back, from cone 13 in front, to a good melted 8 in back. No sidestoking necessary.
I am going to go back to using a pyrometer for the next firing, because this firing got very reduced. I think the stoke intervals were too close, and a pyrometer may help me get a better idea of temp climb timing, and when each cycle goes into oxidation.
At one point, when we switched to stoking the 2nd chamber, the temp just started dropping. You could tell from the sound and color of the kiln. I jabbed a pyro into a peep hole and it told me right away that I was stoking to frequently. After the flame had receded into the chimney and peepholes, and the roar had died away was when the temp really started climbing in the chamber. I had been stoking when the flames receded and the kiln quieted down, but once I started waiting rather for the temp to start dropping after the rise, the kiln got back on track. This rise took longer than I imagined, sometimes up to 10 minutes. Had been stoking waaayyyyyy too much.
This firing was a watershed moment for me, regarding packing, air, and stoking. I think next time will finally be the load that makes us all smile.
Glazes: Glazed ware in the second chamber turned out really nice. Reduction was still too heavy, but we got nice surfaces. Still, I won’t aim for that in the future. Madara glazes were too yellow for my taste. The first chamber glazes were so reduced that whatever their intended color, everything turned out a semi matte green, from the excessive iron pulled from the body saturating the glaze and crystallizing. I think the stoking interval will fix this problem.
Clay body: Oops. Here is where the shit hit the fan. Too much iron, especially considering the temp and amount of reduction that happened. The clay I used for the large pieces has too much iron for that type of firing environment, which is why they almost all collapsed. Having worked with a gas kiln for so long, it is hard to get out of the mindset of adding iron rich clay to other whiter bodies in order to get a desired color. The white clays in this area have enough iron for good color in a wood kiln. I keep forgetting that, but perhaps the shock of this latest meltdown, and the subsequent pain of shelf grinding will serve to jog my memory whenever I’m mixing clay for the wood kiln.