High temperature, smooth, functional, medium plastic, vitreous, light grey-buff burning body made from a mix of refined and clean native clays for reduction and oxidation fired functional stoneware. H555 is a 50:50 blend of our native materials (like those used in H550) and of refined industrial minerals (like ball clay, kaolin, feldspar, silica). It thus features some of the robust drying and working properties of the former while also displaying the more refined and vitreous fired character of the latter.

Process Properties

H555 is one of Plainsman's most pleasant throwing bodies. Although smooth and fine, it is not as slick as bodies made entirely of refined materials. It dries relatively fast and has very high green strength.

H555 has a lower drying shrinkage and thus it dries with less cracking. However, since it is fine grained, extra care and attention in drying are rewarded when making larger pieces, especially flat plates and shallow bowls (i.e. use slip containing an aggregate like molochite, focus drying on evenness rather than speed, use as much pressure and lateral movement as possible when joining, make ware with an even cross section, etc.).


H555 fired test bars. Cone 10R top. Cone 8 to 11 oxidation (bottom upward).

H555 fires to a pleasant light grey-buff in reduction and buff-white in oxidation. It is semi-vitreous (burns to about 1% porosity at cone 10). It burns significantly whiter than H550 (our buff burning native stoneware) and the speckle population and size is much lower. By cone 7 porosity is about 4% so we do not recommend this body for middle temperature functional ware.

H555's high fired strength and homogeneous surface makes it an excellent compromise for fine functional stoneware. But remember that while it is more resistant to warping than our porcelains it is more prone to deforming on overhung or extreme shapes than our native stonewares.


H555 does not bleed iron or interfere with glaze melts and thus encourages clean results. However if you use earthtone glazes that are at their best on iron or speckled bodies, consider trying H550 or H443. If you use white or transparent glazes there will be some scattered small back speckles, especially if the glaze cover is thin.

H555 is easier to fit glazes to than our porcelains but can require a little more effort than our stoneware bodies. Crazing is likely with glazes high in sodium and potassium or very low in silica or alumina. Thus you should watch out for high feldspar low silica/kaolin glazes (these are quite common). High fired strength is one of the important features of this body and this can be severely impacted by a glaze which is under excessive compression or tension. Use a boiling water:ice water immersion test to make sure your glazes fit well. Please contact Plainsman if you need help to adjust your glazes.

H555 with Ravenscrag celadon glaze. Fired at cone 10R.

Glaze Recipes

Consider using our standard G2571A matte and G2947U glossy base glazes as starting points. Information is given on adding colorants, opacifiers and variegators to make any effect you want. You will also find excellent recipes made from Ravenscrag Slip and Alberta Slip (on their respective websites, and For slip decoration, be careful to match drying and fired shrinkage of the slip with the body.

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: C120
 Dry Density: n/a

Sieve Analysis (Tyler mesh):

     +48: 0.0-0.1%
   48-65: 0.0-0.2
  65-100: 0.0-0.3
 100-150: 0.1-0.5
 150-200: 1.5-2.5
 200-325: 5.0-9.0

Fired Shrinkage:

   Cone 8: 6.0-7.0%
  Cone 10: 6.5-7.5
 Cone 10R: 7.0-8.0

Fired Absorption:

   Cone 8: 1.0-2.0%
  Cone 10: 0.5-1.5
 Cone 10R: 0.5-1.5

Chemical Analysis

 CaO       0.6
 K2O       2.0
 MgO       0.5
 Na2O      0.3
 TiO2      0.7
 Al2O3    20.9
 P2O5      0.0
 SiO2     65.5
 Fe2O3     1.1
 MnO       0.0
 LOI       8.3%


Safety Data Sheet

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Logo Plainsman Clays Ltd.
702 Wood Street, Medicine Hat, Alberta T1A 1E9
Phone: 403-527-8535 FAX:403-527-7508