High temperature, smooth, plastic, semi-vitreous, grey-buff burning, general purpose, native body for reduction and oxidation fired functional stoneware.

H450 is suitable for many types of functional and decorative stoneware. Unlike our other high temperature buff stonewares, this material contains no fine sand, it is completely smooth. Where ever possible H450 is preferable H550, H431, H435 and other more expensive white stonewares made from industrial minerals.

Process Properties

H450 has the dry strength and working character of a classic Plainsman native body and will stand up to product handling during manufacture very well. Even though H450 is smooth to the touch it still has a good distribution of particle sizes in the plus 325 mesh range (it draws from the illite, ball clay and kaolinite mineral families). As with any Plainsman native body, H450 has a higher dry shrinkage to plasticity ratio than most refined bodies and anyone who is used to using our bodies is aware of the care and attention to drying needed in making larger pieces, especially flat plates and shallow bowls.


These fired test bars compare H450 (left) with H550. They have been fired to cone 10R (top) and 10, 9 and 8 oxidation.

H450 has a higher porosity that H550 because it utilizes a larger amount of Idaho kaolin than any other body we make (it also contains some fine refined silica powder). Buff bodies made from Plainsman native materials exhibit attractive grey-to-buff variegations at a porosity threshold around 2% (H550 normally fires a solid grey at about 1.6-1.8% porosity at cone 10R). Thus H450 does not fire quite as strong as H550, but for many it is a better compromise between fired maturity, resistance to fired warping, aesthetics and working properties.

H450 is the cleanest burning native material we make. In oxidation H450 burns to a much lighter grey buff than it does in reduction. It will display color variegation in most reduction kilns fired below cone 11. The nature of the variegation relates to radiation of vitreous darker grey color from points where fluxing begins. As firing proceeds these darker grey areas invade the entire buff-colored surface.

Since H450 contains some free quartz, some care is required when heating and cooling it through quartz inversion temperatures, especially if ware is being refired.


Since H450 is high in quartz you can expect it to accept most typical cone 10 glazes without crazing them. Glazes that craze on porcelain bodies will often fit well on H450. It is still possible to get crazing with glazes high in sodium and potassium or very low in silica or alumina. Watch out for high feldspar low silica/kaolin glazes. The nature of Plainsman bodies has permitted the use of such glazes, but they are not balanced. They weaken ware and compromise glaze durability and leach resistance. We recommend a boiling water:ice water immersion test to make sure your glazes glazes will not craze or shiver. One more thing about glaze fit: There is no single thing you can do to improve ware strength better than to make sure glazes fit properly. Poorly fit glazes can cut strength 200%, well fitted ones can double it.

Crazing is very common and it is a sanitary as well as strength and functional issue. Likewise, most potters do not think about glaze solubility in acids and hot liquids or resistance to scratching. If you would like to know how to adjust your own glazes to increase their functionality or to deal with problems like blistered, running, crystallizing, etc. please contact Plainsman.

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

We do not supply a thermal expansion value. The reason is that such numbers often mislead users. First, a body has different thermal expansion characteristics when fired at different temperatures, schedules and atmospheres. Dilatometers are only useful when manufacturers can measure bodies and glazes over time and in the same firing conditions. If a chart is supplied here, please view only as a way to compare one body with another.

Another significant issue is that many customers compare measured thermal expansion numbers with calculated values of glazes in efforts to fits those glazes to a body. This does not work. Calculated values are relative only and have limitations that must be understood. The best way to fit glazes to your clay bodies is by testing, evaluation, adjustment and retesting. For example, if a glaze crazes, adjust its recipe to bring the expansion down (using your account at insight-live), fire a glazed piece and thermal stress it (300F into ice-water). If it still crazes, repeat the process.

If we recommend a base clear or glossy glaze, try calculating the expansion of that as a rough guide to know whether your glazes will fit.

Physical Properties

 Drying Shrinkage: 6.3-6.8%
 Water Content: 22.0-23.5%
 Drying Factor: C120

Sieve Analysis (Tyler mesh):

     +48: tr
   48-65: tr
  65-100: 0.5-1.5
 100-150: 1.0-2.0
 150-200: 5.0-7.0
 200-325: 7.0-9.0

Fired Shrinkage:

   Cone 8: 5.5-6.5%
  Cone 10: 6.5-7.0
 Cone 10R: 6.0-7.0

Fired Absorption:

   Cone 8: 3.0-4.0%
  Cone 10: 1.5-2.5
 Cone 10R: 2.0-2.5

Chemical Analysis

 BaO       0.3
 CaO       0.2
 K2O       1.5
 MgO       0.4
 Na2O      0.1
 TiO2      0.7
 Al2O3    19.0
 P2O5      0.0
 SiO2     68.2
 Fe2O3     1.2
 MnO       0.0
 LOI       8.4%


The inside glaze is pure Ravenscrag Slip and the outside glaze is a 50:50 mix of Ravenscrag and Alberta Slips (see target=_blank for more info). By Tony Hansen.

H450 mugs fired at cone 10R with pure Alberta Slip on the outsides, G1947U transparent (left) and pure Ravenscrag Slip on the insides. By Tony Hansen.

H450 cylinder fired at cone 10R with pure Alberta Slip as a glaze.

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