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lee Jacobson

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About lee Jacobson

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  1. Building a Raku Kiln

    Benzine, A couple of thoughts about raku kiln design. We have built a number of raku kilns over the years and have learned much about what works and what does not work for very long. Here are a couple of tips you might consider: (1) If you can afford it, use expanded stainless mesh for the support cage - there are lots of other materials out there, (steel barrels, concrete reinforcing grid, etc.) for the frame, but it only takes a little heat exposure and frequent firings to oxydise away enough of the steel support to make that you have to start over. Although it is more expensive and heavier, the stainless expanded steel cage that we had welded into a cylinder and folded into a dome shaped top for our raku kiln is now 13 years old and still in excellent shape. (2) If you have a high enough overhead structure above your kiln, I would recommend putting together a counterbalance system to lift the cover for you. If you don't have a structure, perhaps you can build a stand-alone support for it. Either way, it makes lifting your raku cover a breeze. All you need is a lightweight steel cable and cable clamps, two pulleys, and a counterbalanced weight to allow you to lift the cover up and down. Properly counter balanced, it only takes a fingertip to lift and drop the kiln cover. (3) I agree with the 8# density refractory blanket suggestions. Lighter weight blanket works o.k. if doubled in thickness, but will not take as much abuse. Consequently, you will be replacing it soon. We use one layer of double density and it keeps most of the heat inside. (4) Be health conscious - when you work with the refractory blanket be sure to use long sleeves to keep it off of your skin, and wear a respirator mask to protect your lungs. It is nasty stuff. (5) When you push the blanket into place on the inside of the cage frame, be sure to get as much length of blanket into the circumference as you can, compressing it against itself as you lay it into position. This is to help compensate for the shrinkage of the length of the blanket that will take place with repeated firings it is going. Hope this helps. Good luck.
  2. Building a Raku Kiln

    Benzine, A couple of thoughts about raku kiln design. We have built a number of raku kilns over the years and have learned much about what works and what does not work for very long. Here are a couple of tips you might consider: (1) If you can afford it, use expanded stainless mesh for the support cage - there are lots of other materials out there, (steel barrels, concrete reinforcing grid, etc.) for the frame, but it only takes a little heat exposure and frequent firings to oxydise away enough of the steel support to make that you have to start over. Although it is more expensive and heavier, the stainless expanded steel cage that we had welded into a cylinder and folded into a dome shaped top for our raku kiln is now 13 years old and still in excellent shape. (2) If you have a high enough overhead structure above your kiln, I would recommend putting together a counterbalance system to lift the cover for you. If you don't have a structure, perhaps you can build a stand-alone support for it. Either way, it makes lifting your raku cover a breeze. All you need is a lightweight steel cable and cable clamps, two pulleys, and a counterbalanced weight to allow you to lift the cover up and down. Properly counter balanced, it only takes a fingertip to lift and drop the kiln cover. (3) I agree with the 8# density refractory blanket suggestions. Lighter weight blanket works o.k. if doubled in thickness, but will not take as much abuse. Consequently, you will be replacing it soon. We use one layer of double density and it keeps most of the heat inside. (4) Be health conscious - when you work with the refractory blanket be sure to use long sleeves to keep it off of your skin, and wear a respirator mask to protect your lungs. It is nasty stuff. (5) When you push the blanket into place on the inside of the cage frame, be sure to get as much length of blanket into the circumference as you can, compressing it against itself as you lay it into position. This is to help compensate for the shrinkage of the length of the blanket that will take place with repeated firings it is going. Hope this helps. Good luck.
  3. Kiln question

    Hi Ayjay, Years ago we purchased a new electric kiln for our college pottery studio. It had a kilnsitter for automatic firing to the desired cone. We were excited to use it and so loaded it up for it's first bisque. The next morning we came in to discover that the kiln had still not yet fired off and was white hot inside. We turned it off and waited for it to cool. The kiln sitter plate had not been properly adjusted when installed at the factory and consequently it malfunctioned, overfiring the load. It fired so hot that the refractory cement between the bricks of the kiln lid vitrified. When I called the mfg. their first question was "Did you do a test firing as instructed in the owner's manual?" Enough said. Lee
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