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

For many years H550 has been a standard among Plainsman customers for cone 10 reduction functional ware. We maintain the porosity at about 2% for cone 10R. See H450 for a smoother, lighter burning body.

Process Properties

H550 has a fairly plastic but slightly sandy texture and generates plenty of slip during throwing. H550 has a good distribution of particle sizes in the entire plus 200 mesh range (it draws from the illite, ball clay and kaolinite mineral families) to give relatively fast drying and high green strength. However, since H550 has a fairly high dry shrinkage, care and attention in drying are still necessary in making larger pieces, especially flat plates and shallow bowls. If you want a smoother, more plastic body, please use H450 instead.

H550 is somewhat sandy. That means that if you leave water on the surface splits can form when shaping or alteration produces convex contours. Sponge off water and slip on any surface that is under tension (e.g. the belly on a thrown vase).


These fired test bars (left to to right) compare H431, H550 and H435 at cone 10R (top) and cone 11, 10, 9 and 8 oxidation.

H550 is fairly vitreous at cone 10R (the most mature of our bodies made completely from our materials). H450 is slightly less mature and a little more stable in the kiln, it is also smoother, cleaner and lighter burning. In oxidation H550 burns to a much lighter grey buff than it does in reduction. It generally fires solid grey in reduction kilns (cone 10R is past its transition point from reduction light-buff to grey buff).

Since H550 contains some free silica, normal care is required when heating and cooling it through quartz inversion temperatures, especially if ware is being refired.


Since H550 contains more than 70% SiO2 you can expect it to accept most typical cone 10 glazes without crazing them (glazes which craze on porcelain bodies will often fit well on H550). However watch out for high feldspar low silica/kaolin glazes, they can craze on this body (these are quite common). We recommend a boiling water:ice water immersion test to make sure glazes fit well. Please contact Plainsman if you need help to adjust your glazes.

H550 with Ravenscrag celadon glaze. Fired at cone 10R.

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.

Casting Recipe

H550 has soluble salts that prevent the action of deflocculants so it cannot be slip cast. We are working on a casting body that is similar to this one (made from refined materials). You can find information on it here.

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: 6.2.

Physical Properties

 Drying Shrinkage: 6.0-7.0%
 Water Content: 20.5-21.5%
 Drying Factor: C120
 Dry Density: 2.0

Sieve Analysis (Tyler mesh):

     +48: 0-0.3%
   48-65: 1.5-2.5
  65-100: 6.0-8.0
 100-150: 3.0-5.0
 150-200: 4.0-7.0
 200-325: 7.0-9.0

Fired Shrinkage:

   Cone 8: 4.0-5.0%
  Cone 10: 4.5-5.5
 Cone 10R: 5.0-6.0

Fired Absorption:

   Cone 8: 3.5-5.0%
  Cone 10: 2.5-3.5
 Cone 10R: 1.5-2.5

Chemical Analysis

 CaO       0.2
 K2O       1.7
 MgO       0.6
 Na2O      0.1
 TiO2      0.7
 Al2O3    19.0
 P2O5      0.0
 SiO2     69.8
 Fe2O3     1.6
 MnO       0.0
 LOI       6.4%


H550 and glazed with Ravenscrag Bamboo (outside) and GR10-C Ravenscrag Talc Matte (see the target=_blank for more info). By Tony Hansen.

H550 mug fired at cone 10R. Inside glaze is G1947U transparent. Outside is 50:50 calcine:raw Alberta Slip mix. Mug has been fired to 1500F in a decal firing, this has significantly darkened the Alberta Slip tenmoku effect (to almost black).

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