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

Three porcelains and a buff stoneware with transparent base glaze at cone 6.

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 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 vitrify around cone 7 and have just a little porosity at cone 6 (thus it resists warping and crazing while still being very strong). 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, significantly whiter than our P380 but nearly nearly as white as Polar Ice.


More glazes will fit P300 than in the past (because of the higher silica content of its new recipe). Our G2926B Whiteware transparent recipe will fire successfully but it does not survive a 300F:IceWater test (thus long term ware use would likely see crazing). Our G3806C fluid melt recipe and the Amaco Celadon line of glazes have the same situation. The G2934 matte base works well on P300.

We are working on lower expansion recipes. Two promising examples are G3838A and G3813B are among them.

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 Plainsman G2926B clear (inside) and G3806C Copper Blue (outside). 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
Email: plainsman@telus.net