H450 - Discontinued

H450 has been discontinued we recommend H550 as a replacement clay body.


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, H435 and other more expensive white stonewares or porcelains.

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.

Glaze Recipes

Commercial brush-on glazes: They may or may not fit our clays (check for glaze fit using a BWIW test or similar). For brightly colored glazes (especially with layering) do a leach test (e.g. GLLE test). Consider using a transparent or white liner glaze for food surfaces.

Mixing your own glazes is practical (with our clear guidelines even beginners can make dipping glazes that go on silky smooth and evenly and dry in seconds). If you already do this using recipes from the web, be careful. High-feldspar glazes (having more than about 35%) often craze. Some recipes rely on high melt fluidity to encourage crystallization and variegation (often because of inadequate SiO2 and Al2O3 or containing Gerstley Borate or Frit), view these with suspicion for leaching and cutlery marking; test them well (also test the additionless versions). Be suspicious of any glaze not having good documentation.

Consider using our G1947U glossy or G2571A matte base recipes, just add colorants, opacifiers, variegators (you will find links to much more information and pictures about these). If you have a recipe that is troublesome, consider transplanting its opacifiers, colorants and variegators to these bases instead. http://ravenscrag.com and http://albertaslip.com also have many recipes that work well on porcelains.

Crazing: Functional ware must remain craze-free (crazing is unsanitary and drastically reduces ware strength). Even though ware may not be crazed out-of-the kiln it may do so with time. Do cycles of a boiling water:ice water immersions (BWIW test) on a piece to test glaze fit (by stressing it to bring out any crazing or shivering tendencies).

Thixotropy: If you want the best application properties for one-coat dipping, consider creating a thixotropic slurry. Thixotropic glazes are creamy because they have been thinned and then gelled by the addition of a flocculant.

For slip decoration and engobes be careful to match the fired shrinkage of the slip with the body. Where we do not recommend a specific engobe recipe use a one based on the porcelain itself. Add 2% VeeGum or Bentonite (the extra stickiness helps it adhere well to leather hard ware). Be careful about adding fluxes (e.g. frit), this increases fired shrinkage (the mismatch with body can cause flaking) and can compromise opacity.

If you want to develop and mix your own glazes and engobes consider getting an account at insight-live.com. You can organize a methodical development program and adopt better methods of testing (e.g. melt fluidity, thermal stress, slip-fit tests).

Thermal Expansion

We do not supply thermal expansion values. If a chart is supplied here, please view it only as a way to compare one body with another. Please note that, although you may calculate the thermal expansion of a glaze, this cannot be done for clay bodies since they do not melt. The best way to fit glazes to clay bodies is by testing, evaluation, adjustment and retesting. For example, if a glaze crazes, adjust its recipe to bring the expansion down, fire a glazed piece and thermal stress it (using an IWCT test, 300F into ice-water). If it still crazes, repeat the process.

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%


Cone 10R mugs. Plainsman H550. The liner glaze is pure Ravenscrag Slip GR10-A and the outside glaze is a 50:50 mix of Ravenscrag and Alberta Slips (GR10-E). By Tony Hansen.

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

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

Fired at cone 10R. H450 clay. The inside is L3954N black engobe under G1947U glossy transparent. The outside is G2571A silky matte with 5% added rutile to create a bamboo effect. The black engobe appears black under the clear glaze but brown under the bamboo glaze.

Logo Plainsman Clays Ltd.
702 Wood Street, Medicine Hat, Alberta T1A 1E9
Phone: 403-527-8535 FAX:403-527-7508
Email: tim.lerner@plainsmanclays.com