High temperature, smooth, medium plastic, grey-white firing, refined body for reduction and oxidation porcelainous stoneware.

P580 is a variation on the classic '25 Porcelain' mix (25% ball clay, kaolin, feldspar, silica). It uses a blend of 36% ball clays and 12% kaolin to produce a body of greater plasticity. It also has additional bentonite to increase plasticity further. P580 maintains excellent drying properties and is well suited to machine production since it has high leather hard and dry strength compared to porcelains.

While P580 is not quite as white as fine porcelains, it still maintains near zero absorption for functional ware. Thus it is a material-of-choice compared to porcelains if the fired color is acceptable for your application. However, if you can tolerate a slightly darker fired color, we recommend H555.

Process Properties

P580 is a smooth and slick fine grained body that throws and dries quite well compared to all-kaolin porcelains. Its ball clay complement gives it a robust nature that makes it a good choice for machine forming and even hand building. It generates very little slip during throwing and does not work as well when too soft as do more plastic bodies.

However, P580 is fine grained and thus it cannot be expected to dry and handle as well as a coarser stoneware. If you need to join sections, be sure to follow good practice (i.e. use slip containing an aggregate like molochite, dry ware evenly, use as much pressure and lateral movement as possible when joining, make ware with an even cross section).


P580 fired bars. Cone 10R top. Cone 8 to 11 oxidation (from bottom up).

P580 fires darker than P600 or P570. However, its color is stable across the cone 8-10 range in oxidation and its reduction color is quite consistent from firing to firing.

P580 is quite mature (but not vitrified to zero porosity), it contains 24% each of feldspar and silica. It thus produces a very strong product. Thus you must take precautions to make shapes that have inherent strength to resist warping (i.e. avoid goblets with flared bases, flared or overhung bowls). Kiln shelves must also be be flat. You may need to use a little kiln wash to separate lids and vessels.


P580 has a fairly high flint content and is thus easier to fit glazes to than P600.

P580's high strength can be severely compromised if a glaze is under excessive compression or tension. We recommend that you stress-test a piece of ware using a boiling water:ice water test. Ware should be able to survive several two-minute cycles before trouble appears. If you need assistance to adjust the thermal expansion of your glazes, please contact Plainsman.

If you wish to use slip on your ware, make it from a base of P580 itself if possible.

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.

Thermal Expansion Chart. Average: 5.5.

Physical Properties

 Drying Shrinkage: 5.0-6.0%
 Dry Strength: n/a
 Water Content: 21.0-22.0%
 Drying Factor: C110+
 Dry Density: n/a

Sieve Analysis (Tyler mesh):

    +100: 0.0-0.2%
 100-150: 0.0-0.5
 150-200: 0.2-1.0
 200-325: 2.0-4.0

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: 0.3-0.8
 Cone 10R: 0.0-0.5

Chemical Analysis

 CaO       0.2
 K2O       2.9
 KNaO      0.0
 Li2O      0.4
 MgO       0.1
 Na2O      0.8
 TiO2      0.6
 Al2O3    18.9
 P2O5      0.0
 SiO2     70.2
 Fe2O3     0.6
 FeO       0.0
 MnO       0.0
 LOI       5.3%


P580 mugs fired at cone 10R. Pure Alberta Slip as a glaze outside. G1947U clear glaze inside. Glaze employs Grolleg Kaolin (left two mugs) and EPK (right mug). By Tony Hansen.

Large plate by Peter Flanagan. P580 body. The dark slip is colored P600.

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