Two Birds

I was busy cleaning up the yard yesterday, trying to figure out ways to reduce clutter around the studio, and had an epiphany. I could take all of the old electric kiln back up brick that I’d gotten hold of 7 years ago and lay it over the fiber layer on the wood kiln before covering it all up with more mud.

It was a quick, easy decision to make, and actually a quick, easy job. Finished it up in about one half day, and it should add a lot of insulating power to the kiln shell. Best of all, I no longer have a huge stack of orange crates filled with brick, covered with corrugated steel sheeting, sitting at the entrance to the property!

After all, and this is the eerie part, I finished the whole chamber with only a few bricks to spare, plus some unusable fragments. So, the left over brick pile, formerly home to numerous leeches and centipedes, and a few snakes, is now a nice extra layer of insulating brick on the kiln. In truth, the kiln looks like crap now with all of those different bricks sort of jigsaw puzzled on there, but once it has its nice mud jacket on, it will be spiffy and clean looking once more.

The first ‘test’ section.

Continuing to the other side…

All the way to the front, both sides, and the bricks are pretty much gone.

You can see here the mix of bricks, B-1 and C-1 backing brick, and a few inner hot face brick with element grooves. Door lintel areas have some mud/rotten granite/straw mixture to support the bricks. Lots of room left around doors and peepholes to allow a nice thick edge of mud later. The mud mixture is really great, only shrinks 3% from wet to dry, and holds together like cement. Best of all the company will deliver it for about $80 for one ton, or $120 for two tons. It is originally made to be the under layer for roof tiles on old style tile roofed houses and temples/shrines.

Some more improvements

The first firing showed some of the flaws in the stoke hole cover for the front of the kiln, the first being not enough extra overlap around the edges, and the second more dramatic one being the loosening of the frame in the heat, causing the cover to fall out of its frame in the middle of the firing, which was an exciting event.

I cast a new, larger cover for the front stoke, and moved the original to the rear chamber stoke hole, where it is looking quite sharp and happy. The implementation of the frame for the front stoke was done a bit differently, just to see how it plays. I think it will be more stable, balanced and less likely to come apart during firing. At some point, I’d like to do a welded door, but for now this will work.

Here is the cover assembly. I had to drill holes for the rods, but it allows for the angle iron to be oriented across the center line of the slab.

Detail of the angle iron, threaded rod, and shims. My plan is that the shims allow for the angle iron to be tightened to a slight bow, and hence to be in a state of tension, so that when the frame heats up in the firing, there may/will be a loss of tension, but the frame will remain tight and secure around the slab.

Here it is hanging in place. Twisted 2.1mm stainless iwire on the cover assembly. 3.2mm stainless wire twisted around another threaded rod, connected from the overhead beam. In the first firing there was no discernible softening or stretch in the wire (2.1mm) from the heat, so this 3.2mm wire should last a good long time.

The next improvement is by mother nature, who is giving us our first really good bunch of wisteria blossoms:

The coverage is a little sparse, but with a few good prunings over the next couple of years, this little gal should fill in nicely. I’ll post pictures again when the blossoms are in full bloom.

More insulation

Since there were 3 rolls of insulating fiber left over from building the kiln, I decided to use them as added insulation over the first chamber. It took two of the rolls to cover the kiln, with one roll left over for future repairs. This new layer of fiber alone should help a lot with heat loss during firing, and it will be covered with more clay/straw mix, pretty much doubling the insulation over the first chamber.

I found a place in Karatsu that makes a clay/straw/sand mixture that they sell as the base layer for tile roofs. They can ship one ton of the stuff to my studio for about $90, or two tons for $120. REALLY worth it considering the work it takes to mix that much mud and straw. Also, it has much less shrinkage than the regular clay mix I used for the first layer. I made a 100mm test tile to test shrinkage, and the stuff only shrank 3mm from very wet to bone dry.

Here, the first stage is done, with some bricks holding the fiber in place, just in case some high winds come through. I’ll apply the mud in the next week or two, hopefully before the firing happens.

A nice surprise

Yesterday I came home to find a nice surprise sitting in the drive. A 5 inch thick slab of Keyaki (Japanese elm). Last year I had asked a sawmill owner friend of mine if he could locate one for me, and it took a while but he really came through.

I am going to use it to build a new kickwheel, a low wide one that is good for making large pots. Two 20 inch pieces, the flywheel and wheel head, will be cut from this slab, and trimmed round. The hardware will be made from porcelain, rather than tempered steel like my upright kickwheel. I think it will be an interesting project to make things the traditional way.

If you want to see my upright kickwheel, there is a post on it in the archives of this blog.

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Ripe teabowls

Still making work to go in the upcoming firing of the kiln, and tried making some “Komogai” style bowls. Komogai are originally Korean bowls, like Ido, and were emulated later by Japanese potters in Karatsu, Hagi, and probably other areas as well. Below is one komogai gata bowl with feldspar glaze, and one other which is close to komogai in shape, with a rice straw ash glaze. The latter’s name is Hakucho, and it is my favorite Karatsu bowl. It is made of a very sandy clay body, similar, I suspect to Sakamoto san’s clay body (explained below).

I’ve always found these bowls to be very difficult to make, but after today am slightly nearer to understanding them. When one comes out looking right, it is usually still just luck. I discovered today that the best ones look very full bellied, or ripe (this word makes sense to me for some reason).

Just in case you are wondering, I wasn’t trying to make them all the same size. My goal was to work on proportion and shape. When I understand the shape better, I’ll start aiming for more uniform sizing.

The small guinomi, plates, and two komogai at the mid-left were made with clay that I saved from the hole when digging the kiln foundation. It has turned out to be quite nice. I wedged quite a bit of sand into it, to temper it a bit as it is prone to bloat at high temps. The rest of the komogai bowls were made from a fairly refractory very sandy body that I got from Sakamoto san in Sari, Saga. Sakamoto san is one local clay guru who makes clay bodies suited to making Karatsu ware, and all of his clay is made for wood firing. It is nice stuff, but you have to be careful what glazes to use and what temps to fire at.

Two in this row are not komogai shapes, they unintentionally ended up too wide or tall, so I decided to forgo the out-turned lip.

One of the things I’ve been working on is getting work off the wheel that doesn’t require much trimming at all. My mentor, Tsuruta san, can trim boards of bowls and not have much in the way of trimmings in the catch pan. I, on the other hand, have enough to wedge up and make more bowls, which probably means too many trimmings.

This is one of the bowls made from kiln hole clay, it held together nicely despite being stretched wide, though you can see it started to come apart. When making some more open forms, like plates, this clay tended to split and fall apart (two plates out of 10) about 20 minutes after being set out to dry.

Teabowls will become more prominent on this blog in the upcoming months, because the theme for Workshop in Taku, Spring 2012 will be teabowls. More specifically, the making and use of teabowls in Japanese tea ceremony. Official announcement with dates and guest artists/presenters is coming soon.

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Stop signs (long…)

Today I spent a few hours making stop signs. Well, not really. I made bats. The recent discussion about bats on clayart got me to thinking about them, then I got an order for some large beer mugs and realized I needed some bats. Usually all the throwing done on the electric wheel is off the hump, so bats are unnecessary.

Anyway, the whole bat thread started with a little tiff over whether or not bat pins should be standard fare on all wheels. I am a non-pinner, because of the aforementioned hump throwing and although I am not against pins, I am against the exorbitant prices they get here in Japan for bats. More about that below.

During the clayart bat pin death match, David Hendley (a Texas potter) mentioned his bats, which fit around the wheelhead, not on pins. This type, incidentally, are the preferred bats in Japan, but they cost a bloody fortune at around $25 each. No really. They are a breeze to make, so I bought some plywood and went to work.

Plywood at the hardware store was about $16 per sheet and was pre treated on one side with some sort of water proof urethane finish. I got 3 sheets, which made me 24 bats in all.

Cutting the plywood sheets into 40cm squares.

Cutting off the corners, gives a nice stop sign. I could have done circles, but I didn’t have the right bit for my router. If you don’t have means to cut a circle this shape works well. If you are worried about the corners you can keep cutting them until you have close to a circle. My saw horses were lent out, but this ladder on it’s side worked great.

Tap center the bats on your wheel head, and sneak a sharpie under them to draw a circle around the circ. of the wheel head.

Here I used some screws to set blocks in place, to test tightness of fit. They were a bit loose, so later when I attached them for good a jiggled them in over the line just a tad.

Here it is sitting on the wheel.

And underneath view… You can see the cleat contacting the wheel head.

Final gluing. Titebond III is my favorite wood glue. Very strong, water resistant when dry, and no fuss. Cleans up with a wet sponge. I did the first couple with screws to clamp down the wood cleats, but it really wasn’t necessary with the weight method (below) which is much easier.

All the bats finished with 2 pugs of clay ‘clamping’ them down. Make sure all the cleats stack over one another, just like how you stack shelves in the kiln. The first few I put the cleats on with the bats in different directions. Makes no difference in the end, but for this clamping method, it prevents having a cool looking uniform stack. Dang. After the first 7, I finally got wise and assembled the bats oriented the same direction.

Here you can see the cleats lined up in the stack. After a night to dry, they should be good to go!

So, all in all, 24 new bats for about $50 and 3 hours of work. 24 new bats of this type would have cost about $600. All in all a worthwhile project.

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