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…
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.
I like the floor addition so much that I decided to fill the space in completely. It was a quick project and gives us much more space to use upstairs. We now have a place for guests to sleep, although there is still no hot water or toilet in the studio. Still, moving in the right direction. There is room enough to sleep 6 people easily in the studio now.
One problem: all of the lighting is attached to the upper beams, so the floor effectively blocks all light to the 1st floor. Some re-wiring will be done to add lighting to the first floor. I’d prefer to put in brighter lighting downstairs for working, and soft lighting upstairs for entertaining guests, with spot lights added for displayed work.
Oh, and padding for the upper beams, now that they are within forehead striking distance…
I made this table about 5-6 years ago with the intent of using it with guests downstairs in the studio, but as things filled the space I never had a place for it, and it ended up under the staircase for the duration. It had literally never been used for its originally intended purpose and gathered dust. Until a few days ago when I started rearranging the studio. Now with the stairs out of the way, it is out, clean, and ready for action. I scrubbed off 6 years of dust and crud this morning and started thinking about how best to use it.
If you haven’t noticed already, this is a huge grindstone (one of a pair I acquired), and it must weigh at least 200kg. Somehow I was able to get it up on that railroad tie frame with the heavy duty casters underneath so it can be moved. The current top is actually the bottom, and the actual top is slanted, so one side is propped up on two short kiln stilts so the table top is level. The grooves are close enough together that cups can sit without wobbling or falling over.
It occurred to me that the depression in the center would make a good improvised receptacle for tea goodies, and a garbage can could go under the hole for waste disposal. One other suggestion was to place a bamboo section in the whole as a small waste basket. One of the railroad ties partially overlaps the bottom of the hole, so the bamboo doesn’t fall through.
I managed to get my hands on a used wheel, cheap. It is a gigantic banding wheel: wheel head is 50cm across and the whole thing assembled weighs 60kg. It looks like it might have been someone’s homemade wheel, made from acquired parts and put together.
It is an oddly constructed wheel, no bearings at all. The top of the shaft accommodates a pin in the wheel head like my kickwheel, but there is no bearing in the bottom, just tapered sleeve on the shaft that engages the bottom of the wheelhead shaft, heavily greased. It requires a very fine setting of the tapered sleeve. Engage it too much and the wheel doesn’t turn well, not enough and there is a waggle in the wheel.
It arrived pretty rusty and dirty, looks like it saw a lot of use at some point, then got left in a corner somewhere for a few years. I got a wire brush disc for my angle grinder and spent quite a while getting the accumulation of clay, gunk, paint, and rust off.
Finally got the wheel head assembly cleaned up and oiled, and with some experimentation found the ‘sweet spot’ for the tapered sleeve when engaging the wheel head shaft, and the wheel spins quite nicely. Click on the link below to see it spin:
Wheel spin test
My plan for this wheel is to weld arms to the base of the wheel head shaft and mount a wooden fly wheel, and add a wooden wheel head onto the current steel wheel head. The resulting kickwheel should be great for onggi style coil and paddle work.