August 17, 2009
Electric Kiln Firing Techniques and Tips: Inspiration, Instruction and Glaze Recipes for Electric Ceramic Kilns Available for Download!
It’s Monday, and if you are one who notices patterns, you may have noticed that every other Monday lately, we have been rolling out a new free download for our subscribers. And guess what! Today is one of those every other Mondays! Our newest download, Electric Kiln Firing Techniques and Tips: Inspiration, Instruction and Glaze Recipes for Electric Ceramic Kilns, is yours for the taking Ceramic Arts Daily subscribers! In today’s post, I am presenting an excerpt from it, which explains how Satori Yamaoka combines both oxidation and slight reduction to create amazing oil-spot surfaces in his innovative electric and propane kiln. And you can get the full article, plus the others by downloading Electric Kiln Firing Techniques and Tips from our free gifts page. - Jennifer Harnetty, editor.
Electric and Propane Combination Firing
One of the more interesting aspects of Satori Yamaoka’s firing method involves combining electric and propane, a method he has used for about 40 years. He has three electric kilns that go to Cone 9, all of which are designed to allow a small amount of propane to be used at a certain point during the firing cycle.
Using a computer that he has programmed to increase the rate of heat evenly with straight oxidation, electricity is used as the only heat source in the beginning of the firing. At around Cone 08, he introduces a small amount of propane to slightly reduce the atmosphere. This continues to Cone 9, which usually takes 24 hours.
This type of firing has evolved from considerations of cost and the colors Yamaoka wants in the finished ware. The kilns are large, custom-made, rectangular, top-loading electric kilns. The interior dimensions are 159 X 57 X 80 centimeters, (63 X 22 X 32 inches), with about 23 centimeters (9 inches) of brick and fiber insulation. Electric elements are anchored to the fiber hot-face. There are eight exit ports about 3 centimeters (1 1/4 inches) in diameter on the sides, front and back (two on each side). A ratchet-and-cable system lifts and holds the lid open.
Yamaoka fires about 10 electric/propane firings per month. The exact firing schedule varies a lot, but the first part is always electric guided by computer. There are always variables that affect the latter part of the schedule: stacking, which glazes are included, whether saggars are used, etc. So when the propane is introduced, things may change from firing to firing.
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This article is excerpted from Electric Kiln Firing Techniques and Tips: Inspiration, Instruction and Glaze Recipes for Electric Ceramic Kilns, which is free to Ceramic Arts Daily subscribers. |
Kiln Diagrams
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| Top cutaway view of rectangular electric/propane kiln. The manifold that delivers propane to the kiln extends across the length of the center of the kiln floor, with ports every 20 centimeters (8 inches). |
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| Front cutaway view of rectangular electric/propane kiln. Four lid vents draw the propane through the kiln, ensuring even reduction throughout the stack of ware. |
| Kujaku (Peacock) Glaze, Type 1 | Cone 9, reduction |
| Glaze Material | |
| Barium Carbonate | 11% |
| Bone Ash | 2% |
| Magnesium Carbonate | 3% |
| Strontium Carbonate | 6% |
| Whiting | 8% |
| Potash Feldspar | 42% |
| Kaolin | 8% |
| Silica (Flint) | 20% |
| Total | 100% |
| Add: | |
| Copper Oxide | 4% |
| Tin Oxide | 3% |
| Silicon Carbide | 4% |
| Shinsha Glaze, Layer 1 | Cone 9, reduction |
| Glaze Material | |
| Barium Carbonate | 18% |
| Whiting | 7% |
| Potash Feldspar | 38% |
| Kaolin | 12% |
| Silica (Flint) | 25% |
| Total | 100% |
| Add: | |
| Red Iron Oxide | 1% |
Tags: Electric Kiln Firing Techniques, High Fire Glaze Recipes, Kiln Plans and Diagrams
Laurie | August 18th, 2009 at 12:24 am
Are these Glazes food safe with the Barium Carb. in them?
Jennifer | August 18th, 2009 at 10:53 am
Laurie-
Because of the many variables involved in glazes (clay body and glaze fit, variability in chemical content, temperature uniformity in kilns, organic materials, etc.), we cannot guarantee food safety. The best way to be certain is to have one of your finished pieces leach tested by a lab. Here are some resources for you:
http://www.digitalfire.com/services/consultants/index.php
http://digitalfire.com/services/database.php?list=labs
-editors
Steven | August 21st, 2009 at 3:58 pm
Laurie,
With respect to the editors, they really are not food safe. Barium in that % is quite high and it is unlikely that the fairly normal levels of silica protect the Barium from potential leaching. They are correct in saying though that there are so many variables that go into that you can only ever be sure by testing your own situation.