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H570

High temperature, smooth, plastic, semi-vitreous, white to grey-white burning, refined material body for oxidation and reduction fired functional stoneware.

Unlike our porcelains such as P580 and P600, H570 is semi-vitreous (is not zero percent porosity at cone 10 and 10R). It employs high quality ingredients and utilizes five clays and two feldspars to minimize effects of individual material changes. Plainsman also offers a similar middle temperature body named M370.

Process Properties

H570 offers excellent plasticity even if the material is very soft. Also, most users will find that it has a different plastic quality about it. This is due to the incorporation of a unique plastic feldspar from California that offers a rare combination of very white fired color, low melting point and a particle size profile that meshes very well with the existing kaolins and ball clay in the mix. This allows us to create a body with minimal fluxes (i.e. feldspar), maximum clay content, and a much better drying behavior than is normal for this level of plasticity.

This is a fine grained material, so our recommended standard drying practice will be beneficial. H570 may tend to warp during drying so you might need to dry ware slower and more evenly.

Firing

Although H570 does burn white and speck-free, it does not reach zero absorption during firing to cone 10. However it does fire more dense in reduction than in oxidation. H570 has a fired surface and strength more similar to stoneware than porcelain and is thus better suited to firing conditions that are not totally consistent. Compared to vitreous stoneware or porcelain, lids will display less tendency to stick to the lips of containers during firing and overfired ware will be less likely to warp, bloat, or glue itself to shelves.

However there is an important caution: H570 is quite high in free quartz. This is an asset to achieving glaze fit but also means that you should not cool the kiln through quartz inversion temperatures (e.g. 1024F) too quickly during firing or dunting cracks will occur (especially in large bowls and plates). You will note from the expansion curve (smooth at 220C 428F) that H570 does not appear to form significant cristobalite despite the fact that it is semi-vitreous. Remember also that cooling your kiln too quickly through any stage may set up temperature gradients within pieces that will continue even if you attempt to slow-cool during certain ranges.

Glazing

H570 will preserve bright glaze colors without the iron-bleeding problems associated with stonewares. However, if you wish to use glazes with earthtone shades, consider one of our darker burning materials.

Since H570 has a makeup somewhat different than our other porcelains and white stonewares, it is not guaranteed to work with the same glazes and slips. Test thoroughly before committing to using large amounts. Since H570 is very white, try to use H570 powder as the base for any slips that you apply.

H570 has some porosity so penetration of water is demonstrated. Make sure your glazes are fitted to the clay by stress-testing ware (using the boiling water:ice water method) to bring out delayed crazing. If you need assistance to adjust the thermal expansion of your glazes, please call Plainsman.

Glaze Recipes

You can develop a compatible glossy or matte base for this body from our suggested starting point base recipes available on our Internet web site at http://digitalfire.com/education/glaze/cone10.htm. Information is given on how to fit the glaze to your body and how to customize it 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.

Thermal Expansion

The chart shown was produced from a specimen fired once to cone 10 reduction in the Plainsman lab and tested in an Orton dilatometer. If you fire to a different temperature, employ different heatup or cooldown rates, or glaze-fire more than once the thermal expansion in your ware may be different than this chart indicates.

Thermal
Expansion Chart
Average: 5.7

Physical Properties

 Drying Shrinkage: 5.5-6.5%
 Dry Strength: n/a
 Water Content: 21.5-22.5
 Drying Factor: C130
 LOI: 5.0-6.0%
 Dry Density: n/a

Sieve Analysis (Tyler mesh):

     +48: 0.0-0.1%
   48-65: 0.0-0.2
  65-100: 0.1-0.3
 100-150: 0.1-0.4
 150-200: 1.5-2.5
 200-325: 8.0-11.0

Fired Shrinkage:

   Cone 8: 6.5-7.5%
  Cone 10: 7.0-8.0
 Cone 10R: 6.5-7.5

Fired Absorption:

   Cone 8: 2.0-3.0%
  Cone 10: 1.0-1.5
 Cone 10R: 0.3-0.8

Chemical Analysis

 CaO       1.2
 K2O       2.1
 KNaO      0.1
 MgO       0.3
 Na2O      0.9
 TiO2      0.4
 Al2O3    19.2
 P2O5      0.0
 SiO2     68.4
 Fe2O3     0.5
 FeO       0.0
 MnO       0.0
 LOI       6.8%

News

H570 is made entirely from refined materials that we import from different parts of North America. We see regular changes in the degree to which these materials vitrify, their plasticity, and their fired color. It is a challenge to deal with these changes so that the body is stable, however H570 has a recipe that draws on many different clays and feldspars to spread the risk and enable adjustment to compensate. We see the most variation in a plastic feldspar and a ball clay and have been making small changes to the bentonite content to compensate.

Plainsman Clays Ltd.
Box 1266, 702 Wood Street, Medicine Hat, Alberta T1A 7M9
Phone: 403-527-8535 FAX: 403-527-7508

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