Plainsman Native Materials

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• Boraq - Plastic borate (substitute for Gerstley Borate)
• Ravenscrag Slip - Fine grained low plasticity cone 10 melting silty clay
• Alberta Slip - Low temperature fusible clay for high temperature glazes
• Helmer Kaolin - Moderately plastic kaolin mineral used in wood firing bodies and as a source of halloysite
• B Clay - Light-buff Stoneware
• Midstone - Grey-buff Medium Stoneware
• Palestone - Grey-buff High Temperature Stoneware
• Plainsman Fireclay - Plastic Fireclay
• Kaosand - White Kaolinized Sand
• Redstone - Red Burning Medium Stoneware
• Firered - Red Burning Fireclay
• Plasticfire - Refractory Ball Clay
• Tapper II - Furnace Tapping Clay
• 3D - Silty Light Tan Medium Stoneware
• M2 - Red Burning Medium Temperature Raw Clay

The Plainsman Clay quarries produce a wide variety of materials that are well adaptedto ceramic plastic forming processes. These materials have a number of advantages:

• Plainsman Native materials are specifically selected for pottery body applications.
• You can add water to most Plainsman Native materials and use them as is without trouble. Formulating with them is not a constant balancing of materials that are useless in themselves and which have to be balanced against opposites; highly plastic against totally non-plastic, high fluxed against highly refractory, very smooth against very coarse.
• Bodies made from balanced raw materials are easy to formulate and adjust, the results are predictable, it is generally just a matter of fine tuning a clay body to your exact needs after one or two preliminary mixes.
• Bodies made from balanced materials are much more tolerant of slight variations in individual materials.
• Many Plainsman Native Materials contain natural fluxes and the lighter colored stonewares mature as low as cone 8 without the need for feldspar.
• No red iron oxide will be needed for your darker bodies as dark burning Plainsman Native Materials contain iron in its natural, and much cleaner, form.

Working and Drying Characteristics

In general you will find that our clays provide a wide range of plasticity and particle size properties. Each emphasizes are particular property (e.g. color, texture, plasticity,maturity). The only clay that is too non-plastic to actually use straight is Kaosand, the only one that is too plastic is PlasticFire. The rest are balanced enough to produce ware with no further additions.

Our clays have a fairly high drying shrinkage if they blended for plasticity(6.5-7.5%). At the same time they tend to have an extremely high dry strength (typicallydouble that of most refined alternatives). Thus bodies made purely from our materials will not dry quite as well as those that can be made from refined materials. However, minimal additions of kaolin, fine grog, or other materials can lower the drying shrinkage while maintaining plasticity.

Bodies made from Plainsman Native Materials tend to dry fairly fast compared to those made from refined materials. This is because the larger particle sizes tend to vent ware better.

Plainsman Native Materials contain a small amount of barium carbonate to precipitate soluble salts that might otherwise affect the fired surface and interact with glazes. This results in a clean fired surface, free of patchy discoloration often seen in ball clays,fireclays, and some kaolins.

Firing

Since Plainsman Native Materials are not ground to 200 mesh particle size, they do contain some particles that will cause specking in some firing conditions. In general, the higher a material is fired, the more its speckle will develop. At the same time, most of our materials are very clean, nature has cooperated in removing mechanical impurities during sedimentation of the deposits we mine from.

Many of the Plainsman materials are quite high in free silica. On one had you will find that this prevents crazing by helping to put compressive force on glazes. On the other hand, it can mean that bodies are a little more susceptible to thermal shock failure as the materials pass through quartz inversion temperatures. Since most bodies made from refined materials have significant amounts of quartz added, you will find it refreshing that little or no quartz needs to be added to our materials to make them fit common glazes.

Many of our clays contain natural fluxes that make them mature at a relatively low temperature. It is entirely feasible to produce bodies at cone 8 and above that have no feldspar (although you might like to use a little to bring into solution any cristobalite that might develop during firing).

Glazing

Since Plainsman Native Materials are not fine-ground to 200 mesh bodies employing the coarser materials (i.e. kaosand, fireclay) in the lower and medium temperature ranges can pinhole some glazes. This happens because these tend to produce a bisque ware product with an internal network of channels and gases of normal decomposition produced during firing are vented at fewer sites of greater volume. Glazes can become overwhelmed as these gases bubble through and thus have difficulty healing over the disruptions. In these cases consider using the finer materials like Palestone and Midstone, use glazes which do not have an excessively stiff melt, or make sure users soak firings. Some of the coarser particles in our native materials also tend to produce significant gases and some can melt vigorously. If these particles are just under the surface they can produce a minute hole in the surface that some glazes are reluctant to run in and fill. This problem can usually be dealt with by making sure that bisque temperature is as high as possible to burn these materials away before the glaze firing, that there is plenty of air flow through the bisque kiln, and that the bisque kiln is maintained in a strongly oxidized atmosphere.

Plainsman Native Materials have a very high green strength and thus are quite viable for single-fire glazed ceramics. For such uses we recommend that you condition your glazes to gel somewhat to achieve an even layer without the necessity to immerse pieces for lengthy periods.

If you need to develop a glaze for any body made from Plainsman Native Materials, we suggest you check our suggested starting point base recipes available on diskette, inprint, and on the internet. Information is given on how to fit the glaze and how to customize it for colors, opacity, speck, variegation, etc. For slip decoration, be careful to match drying and fired shrinkage of the slip with the body since low temperatures generate little glass to adhere the slip. Call Plainsman for complete slip and glaze formulation information if needed.

Physical Properties

Because our native clays are quite balanced, in most cases we perform the same lab tests as with our prepared clay bodies. If you would like more information on how these tests are done, see the over section of our Product Guide book.

Plainsman Clays Ltd. 702 Wood Street, Medicine Hat, Alberta T1A 1E9 Canada

Phone: 403-527-8535 FAX: 403-527-7508