In a recent massive cleaning around and in the studio, I changed things around to utilize some of the outside space more efficiently. One of the most important things is that I now, again, have a setup for processing clay and ash that I have collected and burned.
I had been getting close to finishing off my stores of collected clay that I processed some years back, time to start doing it again. I think I have a better system this time, and I have an inexhaustible supply of pine ash for now, too.
I have buckets, bags, and jars full of old collected clay and dry trimmings that need recycling. It should take some months to get it all blunged and pugged.
Collected clay that has literally been sitting around for years.
The Choppage ‘cho’ ‘pah’ gay’, is a traditional Korean tool for scooping off clay and other materials without disturbing everything underneath. It works much better than a ladle. I couldn’t find anyone who made them anymore, but my mentor still had one which is kindly letting me borrow.
Clay washing bucket setup, and scooping tool, called choppage.
I just agitate the material in the bottom bucket, wait, and scoop off the stuff that settles last.
Then, later after it settles in the upper bucket, I siphon the water back down into the main bucket. When enough of the upper bucket fills with material, I dump it into cloth lined basket or plaster to get out the excess water.
After returning water back into the main bucket from the ‘good stuff’ bucket.
With the ash, the process is the same, but after I get out the good fine ash I transfer it into another bucket and wash it some more to get out the nasties. The nasties cause problems with glazing sometimes and I don’t like them. I do save the water containing the nasties for other uses.
Pine ash bucket setup, main on bottom, fine up top.
The leftover rough ash stuff seems like a waste to just throw away, so I am thinking about ball milling it to see if it can be useful in some other way. We’ll see…
The leftovers after the good stuff is scooped off.
Scooping with the choppage tool.
The sieve is 120 mesh, because I lucked into a cheap recycled sieve. I would usually use 100 mesh, so it is not much of a difference.
Dumping through sieve which is sitting on the bucket mouth.
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.
Hiura
Himae
Front of rear setting, front chamber
rear chamber, very hot
The whole bunch of it
rear chamber, top
firebox
firebox
firebox
front chamber, rear top of front setting
mid setting of front chamber
almost not enough heat for Ao-Yu
mid setting of front chamber
mid setting of front chamber
mid setting of front chamber
front of rear setting of front chamber,
clear over ame-yu works
mid setting of front chamber
mid setting of front chamber
mid setting of front chamber, more glaze shoulder level and higher
Very front, bottom
Very front, bottom
Very front, bottom
rear of front setting, bottom
rear of front setting, bottom
mid of front setting,
mid of front setting,
front of front setting,
mid of front setting,
front of front setting,
mid of front setting,
mid of front setting,
Tameike w/clear,
try taishu feldspar glaze next time
Tameike w/clear,
try taishu feldspar glaze next time
Tameike w/clear,
try taishu feldspar glaze next time
Hanjiki w/clear,
try taishu feldspar glaze next time
Tameike w/clear,
try taishu feldspar glaze next time
Hanjiki w/clear,
try taishu feldspar glaze next time
Ao-yu reacts strangely with Oshima white, too matte
Ao Yu on hanjiki,
Madara on Karatsu Daishizen
rear side
fire side
rear chamber, under fired. Soak at high temp necessary!
rear chamber, under fired. Soak at high temp necessary!
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.
We got this off the shelf in one piece! The attached cup sits level when you set the piece on a table, so great for sashimi and sauce or condiments.The Fall of IcarusArm detail
… some pictures of new fired/finished work. Finally got my brightness and white balance issues resolved and took a few pictures to share with everyone.
I finished the deco on the cups from the previous post a couple days back, and glazed them. After doing the iron brush deco, I gave them a THIN coat of clear glaze, very watery: about 32 on the hygrometer. The deco images were visible under the glaze when it was still wet, though once dry it was no longer transparent.
Here are the images of one of the cups before the glaze was applied.
When Nishioka Koju passed a few years ago, a friend of a friend got some of the warehoused clay from one of Koju san’s storage areas. I was able to get about 60kg of raw dry clay and have been waiting for the right opportunity to use it. I tested it a couple of years ago in the gas kiln and decided it needed wood to really make it jump. The clay itself is a light grey, almost white when dry, so I thought it might be fairly low in iron, but tests showed it to have significant iron and not very refractory. Probably good at around cone 6.
I made a run of about 40 cups yesterday and trimmed them this morning, then waited for them to firm up a bit. Then, in the afternoon I applied the white slip (kohiki). This was something I have never done before on wet greenware. Last firing I tried it on dry greenware with success, but that clay was different and pretty stable for raw glazing. This clay is quite different so I didn’t know what to expect. Many sources say to slip the inside, then let it dry, then slip the outside, to prevent the pot from collapsing. The problem with this is that you end up with too much slip around the lip of the pot, and more work is required to clean it off. I decided to apply to the whole piece at once, and did just one test piece to see what would happen. After 30 minutes the pot was still in one piece so I went ahead and did the whole group of 40.
I really like what the slip does on a wet pot. There is a lot more flow and variation in thickness, and I suspect better adhesion too. After the slip dries I will do some brush deco and give them a thin coat of clear.
At the end of the hump, there was enough left for a teabowl, so I threw one. It is intended to be a Todoya style Korean bowl, but we’ll have to see what happens in the firing. At least, this clay trims real nice. Unfortunately the bowl would not hang on to the trimming chuck, so that is the reason for the abrupt end on the interior of the ring. So as not to end up with nasty chuck rash, coupled with over trimmed foot syndrome, it got left as is. Usually trying to fix something like this just ends in disaster…
foot on teabowl, a little too beefy because I screwed up.
Todoya teabowl
happy cups
Victory! All slipped and having sat for 40 minutes or so, probably not going to sef destruct.
slightly different variation
closeup. this is modeled after my favorite yunomi. 400 years ago this design was for food dishes, but work great as teacups too.
