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Finished firing

After taking things slow for about 12 hours, we took the kiln up to cone 11 over the next 24. Finished up at about 4am Saturday morning, quite a bit earlier than I had planned. Earlier in the firing, I had thought it would take longer, because the kiln was not really responding to the stoking and seemed to be reducing strongly, making me think that I’d perhaps closed the flue channels a bit too much prior to firing. However, after cone 9 started to finally go down, we started to get that great growling roar following every stoke, and pretty soon cone 11 was bending. Here are some sequential pictures from the firing.

Nakayama kun stoking under the grates during the preheat, we kept it at around 250C or under for about 12 hours.

 After we got to about 1000C, we started getting smoke.

 The castable on the second chamber splitting along the line I was hoping for….

 Cone 11 is half over and Nakayama kun is starting a stoke.

 It almost feels as if the flames will push the stoke cover away from the kiln wall. Without the rod propped against the cover, the flames come out in all directions.

 The chimney after the stoke, it is about 3 am.

 After I clammed up the kiln for good, there was still enough fuel in the form of embers to keep burning pretty strongly. I was  a little worried about inadvertently over reducing when I saw this. Not sure if this was good or not, I decided to open up the rear damper again and let some of those excess calories exit the kiln, however the extra oxygen just cause the temp to start rising again and after about 10 minutes I shut the damper again. By then the flames subsided quite a bit.

 Here is the door all mudded up, because there was a good 5mm space all around the door where the kiln had expanded.

Notes from this firing:
-I may need to open up the flues a bit to get some more air flow.
-The insulating castable on the front wall and rear chamber is AWESOME! Even at cone 11, I could keep my hand on the castable surfaces.
-Pyrometers are not to be trusted. The highest reading I got the entire firing was 1056C, and this was when cone 6 was about half over. Moreover, as the kiln got hotter the range of the pyrometer readings actually became lower and lower. Not sure what this means yet. I’m thinking right now that the pyrometer is not extending into the kiln far enough, and pretty much is just responding when directly exposed to flame.

We will be unloading on Wed. I will post pictures shortly after… I can’t wait…

Taking it slow. . .

It is three in the morning and the fire is burning along nicely . A lot of greenware in the kiln this time, so we are very relaxed right now, going slowly. It is a nice feeling to be the only one up this time of the morning, I can hear the faint intermittent roar of cars on the highway in the distance, but other than that it is just the crackle of the fire. Later today, it is going to get pretty hot and busy, so just enjoying the moment for now.

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waterlogged

It continues to rain here, rained cats and dogs all night. This was the state of things in the morning:

You can see the shelves laying across the door above the primary air. The second one down is the same level as the kiln floor. Pretty darn close to flooding, but safe. It rained A LOT, all night, and I’m not sure why it stopped at this level. It usually stops around here so there must be some sort of drainage happening that keeps it from coming higher.

I am somewhat encouraged by this because it means I can finish loading today and probably not have to fear that pots will be floating out and about tomorrow morning.

Oh, and there were no dead animals in my kiln this morning, always a plus.

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.

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.

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Cutting the plywood sheets into 40cm squares.

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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.

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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.

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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.

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Here it is sitting on the wheel.

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

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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.

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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.

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

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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.

Fishing, not clay today…

It was my eldest son’s birthday, and he requested we go fishing. It has become a sort of birthday ritual for us by now and we have a great time, especially when we catch fish. Today we did pretty well. Our neighbor’s daughter came with us, she is a fishing machine! Total concentration.
Two Bream and 7 small Yellowtail were the catch of the day. I lost 2 large Yellowtail, one to a weak leader line, and the next to a hook that wasn’t set properly. Fought it for a good 3 or 4 minutes before it shook the hook off. I’m still frustrated about that one. It came up high enough once that we could see it and it was probably about a 12 pounder. Aargh!

Here are some of the flowers starting to bloom in the garden/area.

 Cherries in the park at about 60% open.

Weeping fruitless peach in our yard, with nice bright colored buds.