Mid-temperature, medium plastic, vitreous, off-white burning, kaolin-only porcelain.

Plainsman Polar Ice, P300, M370 and M340 (Whiteware transparent glaze on the porcelain, Stoneware transparent glaze on the M340).

P300 is a mix of plastic Georgia kaolin, nepheline syenite, 25% silica, raw bentonite (to augment plasicity) and a small amount of talc (for fired maturity control). P300 is not translucent at cone 6. It is the whitest body we can make without using expensive white plasticizers or overseas kaolins.


New Recipe September 2015: We have increased the silica in the P300 recipe from 17% to 25%. This makes it easier to fit glazes (crazing was an issue in the past). Plasticity and workability have been improved by a shift to a more plastic kaolin and a further bentonite addition (drying performance is still excellent).

Process Properties

P300 is a smooth, slick and fine grained. Since it relies almost entirely on plastic kaolin for workability the pugged material has a unique distinct feel that many prefer to high ball clay porcelains. Because of the added bentonite, plasticity is excellent (as good or better than M370).

P300 is a porcelain, so it does not dry as as well stoneware (but the drying is still good, most people will have no trouble with typical ware). Of course, large flat plates and tiles will require extra care. The key to success is to prevent gradients in water content across the ware during all stages of drying (at no time should one part of a piece by significantly drier than another).


P300 fired bars. From cone 4 (bottom) to cone 7 (top).

P300 is intended to have just a little porosity at cone 6 (to give some resistance to warping and crazing). It has a fairly high fired shrinkage so ware must be able to slide against the shelf to prevent warp and sticking (of course it is wise to kiln wash the shelves also). Endeavor to make ware of even cross section, this will produce inherent structural strength to resist warping.

P300 fires a little whiter than M370 but nearly nearly as white as Polar Ice.


We stock commercial cone 6 bottled glazes in many colors and surfaces. However you should check for glaze fit to assure the highest quality ware. For food surfaces (and lower cost), it may be better to mix your own glazes. Develop or adopt a good transparent base and add colors and opacifiers to it. For best quality, consistency, slurry workability we recommend avoiding recipe fluxed with Gerstley Borate, use frits. We supply (as products and recipes) transparent glossy whiteware and matte frit base glazes. Their documentation describes how to mix, use and fire them and showcases stain and other additions to create an infinite number of effects.

Crazing: Function ware you make must remain craze-free for years (crazing is unsanitary and drastically reduces ware strength). Do a boiling water:ice water test to check for it. M370 and Polar Ice fit our recommended base glossy and matte glazes (mentioned above). P300 is the most difficult. More glazes will fit it than in the past (because of the higher silica content of its new recipe). The G2934 matte base works well on P300. However, while our glossy whiteware recipe fires without crazing on P300 it does not survive a 300F:IceWater test (thus crazing would appear over time). We are working on lower expansion recipes. Two promising examples are G3838A and G3813B are among them.

Our standard whiteware glossy may not have a enough melt fluidity to create reactive visual effects for additions of certain colors and variegators. The G3806C fluid melt recipe is an alternative (however crazing can be an issue, especially on P300).

Glaze slurry consistency and quality: A secret to achieving even glaze coverage is controlling the thixotropy of the slurry (prepare a more-fluid-than-normal glaze slurry and flocculate it to gel it slightly). In the gelled condition the glaze goes on much more evenly, does not drip and can be applied in a thinner layer (for more information google "glaze thixotropy"). Always screen glazes when first making them (80 mesh). Be alert to any particulate that may appear after storage (e.g. precipitates) and screen again if needed.

For slip decoration be careful to match the fired shrinkage of the slip with the body. We recommend using a slip (or engobe) recipe based on M370 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 and can make the slip translucent. Stains can do the opposite (lowering fired shrinkage).

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: 5.0-6.0%
 Dry Strength: n/a
 Water Content: 21.5-22.5%
 Drying Factor: c110
 Dry Density: n/a

Sieve Analysis (Tyler mesh):

     48-65: 0.0-0.1%
  65-100: 0.0-.1
 100-150: 0.0-0.1
 150-200: 0.3-0.8

Fired Shrinkage:

 Cone 5: 6.5-7.5%
 Cone 6: 7.0-8.0
 Cone 7: 7.5-8.5

Fired Absorption:

 Cone 5: 2.0-3.0%
 Cone 6: 0.25-0.75
 Cone 7: 0.0-0.25

Chemical Analysis

 CaO       0.3
 K2O       2.1
 KNaO      0.1
 MgO       0.1
 Na2O      0.6
 TiO2      0.8
 Al2O3    25.1
 SiO2     63.1
 Fe2O3     0.3
 FeO       0.0
 LOI       6.6%


P300 (left) and M370 mugs with G2926B clear glaze and black outer glaze (G2926B+black stain). By Tony Hansen.

P300 with Alberta Slip base glaze. But this employs 20% frit 3249 (instead of 3134) producing a lower thermal expansion.

P300 and M370 Cone 6 mugs. By Tony Hansen. Outside glaze is G3806C plus copper oxide.

P300 and M370 mugs with GA6A Alberta Slip at cone 6 (glaze uses Frit 3249 instead of Frit 3134). Firing soaked 30 minutes at 2100F on the way down and slow cooled 100F/hr down to 1400F. By Tony Hansen.

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