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| H440 - Dark Red-brown Speckled Iron Reduction Stoneware | |
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H440G - Dark Red-brown Iron Reduction Speckled Sculpture Body |
| H443 - Brown Speckled Iron Reduction Stoneware | |
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H441G - Buff-white Grogged Sculpture Body |
| Sculpture Clay - Heavily Grogged, Plastic, Dark Burning | |
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| H431 - Grey-buff Sandy Reduction Speckled Stoneware | |
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H435 - Grey-buff Stoneware |
| H550 - Grey-buff Functional Stoneware | |
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H450 - Grey-buff Smooth Stoneware |
| H555 - Grey-white Functional Stoneware | |
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H570 - White Plastic Semi-Vitreous Stoneware |
| P580 - Grey-white Porcelainous Stoneware | |
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P600 - Porcelain |
| P700 - Grolleg Porcelain | |
High temperature pottery is the easiest to work in and the ware produced is generally the hardest and strongest (although this is not always the case). High melting plastic clays can be employed in much greater amounts in the clay bodies; bodies thus tend to be much more plastic.
Plainsman has a unique suite of raw materials which we mine from quarries across the prairies. Most vitrify in the cone 8-12 range and thus lend themselves very well to the production of buff and dark bodies that mature around cone 9-10. Generally this can be done without the addition any raw feldspar or flint.
High temperature clay bodies tend to have the best workability because they do not require as much feldspar and other fluxes in the recipe. Many more materials melt at higher temperatures and thus glazes are much easier to formulate and maintain. Most of our high temperature bodies are made from 100% native materials and they showcase the best aspects of these materials.
There tends to be a 'mistique' around high temperature firing that stems from the fact that the atmosphere in fuel burning kilns tends to produce less consistent results from firing to firing and there are more 'surprises'. In addition the 'earthy' and 'metallic' effects seem to come more naturally in such kilns. Still, much of the ware being produced can be made in medium and low fire (fuel or electric) in a much more economical way without sacrificing too much strength. In fact, in some cases (i.e. iron stoneware) lower temperature vitrified bodies are stronger. However, the lower you fire the more expertise is required to make your own glazes work well.
High temperature firing is generally more suitable for the production of ovenware and other items which must withstand thermal shock. Firings can be tailored to reduce certain mineral phases that have high expansion properties and glazes can be fitted and interfaced better.
Compared to other temperature ranges, cone 10 is very 'glaze friendly'. The high heat available will melt many more ceramic minerals and thus not as much flux is needed. This means that much more silica and alumina can be used in recipes and glazes can be made totally from raw unfritted and inexpensive materials. In addition glazes fire harder, develop a good interface with the body, are much easier to fit to clay bodies, and soften and melt over a wider range of temperatures. Raw glaze properties are better also since more kaolin and other high-melting clays can be employed to harden the dry glaze layer and suspend the slurry.
Reduction firing is common at high temperatures, and is used mainly to bring out earthtone colors of iron or the reds of copper. Most glaze bases however will fire well in either atmosphere. Note that high temperature metallic stained glazes generally do not burn to the same bright colors that can be achieved in the lower ranges.
Since much functional ware is fired at high temperatures, it is important that your glazes fit your clay body, from a ware strength, aesthetics, safety, and functional point of view. Do not make the mistake of judging your glaze as fitting because there are no visible signs of trouble. A simple boiling water:ice water cycle test (of two minute duration per switch) is suitable to bring out most crazing or shivering. If you need help to match a glaze and clay or strengthen your ware (doubling the strength is not unusual with a better fitted glaze), please call Plainsman. We can supply information and tools to adjust your own glazes.
We do not recommend that you have more than two or three base glazes (one is ideal). It is better (and cheaper) to understand how to adjust one glaze to vary its color, surface, expansion, character, etc. than to have twenty recipes that you cannot control.
Visit the web page at http://digitalfire.com/education/glaze/cone10.htm for a good glossy and matte base glaze with lots of information on controlling the two to create any effect you want.
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Plainsman Clays Ltd. 702 Wood Street, Medicine Hat, Alberta T1A 1E9 Canada |
Phone: 403-527-8535 FAX: 403-527-7508 |