Midstone

A fine grained, medium plasticity, buff burning native stoneware material reaching vitrification and very high strength at cone 7. Midstone is a very balanced smooth stonewre material mined in southern Saskatchewn. Midstone and Palestone are the most balanced and highest quality stoneware clay raw materials in North America and there are huge reserves of both (Midstone is less plastic than Palestone and lighter firing). Using a mix of Midstone and Palestone is an ideal way to assure a consistant body year after year. Midstone is available in raw lump form, please enquire.

Many of our bodies, including M340, H550, H460 and L212 contain significant amounts of this Midstone and Palestone.

Process Properties

From a working properties point-of-view, Midstone is well balanced enough to be suitable as the main constituent for middle and high temperature bodies. In fact it is quite useful as a body all by itself. It can also be considered a plasticity-neutral addition to existing bodies.

Midstone contains a small amount of ball clay that we can increase or decrease to compensate for changes in plasticity. It also has a small complement of 3D silty stoneware to provide adjustability to maintain texture, particle size, and drying properties.

Midstone contains soluble materials that are hostile to the deflocculation process, thus it cannot easily be used in casting slips.

Firing

Midstone burns to a light straw color at cone 4 and progresses to a solid light grey-buff at cone 7-8.

Midstone-based bodies offer several advantages:

Midstone vitrifies and reaches maximum fired strength around cone 7-8. Thus is it entirely feasible, even desirable, to make Midstone-based stoneware bodies that contain no feldspar at all.

Unlike many other stoneware clays, Midstone is very clean and speck free for a material ground only to 40 mesh. Even reduction firing does not bring out significant iron blossoms.

Midstone is fairly high in free silica, so bodies employing a significant amount may require no added flint.

Midstone contains a small amount of talc used to control its maturity. In the event that the mix becomes more refractory or more vitreous we increase or decrease the talc to compensate.

Glazing

Bodies made from Midstone are easy to fit glazes to. A typical glaze that fits Midstone will tend to craze on porcelain.

Thermal Expansion

This chart was derived from a specimen fired once to cone 6 in the Plainsman lab and tested in an Orton dilatometer. It is a general guide only. If you fire to a different temperature, employ different heatup or cooldown rates, or glaze-fire more than once the thermal expansion in your ware may be different than this chart indicates.

Thermal Expansion Chart
Average: 6.0

Physical Properties

 Drying Shrinkage: 5.0-6.0%
 Dry Strength: n/a
 Drying Factor: C110
 Dry Density: n/a

Sieve Analysis (Tyler mesh):

   48-65: 0.2-0.7%
  65-100: 0.2-2.0
 100-150: 1.0-3.5
 150-200: 2.5-5.5
 200-325: 5.0-9.0

Fired Shrinkage:

  Cone 4: 3.0-4.0%
  Cone 5: 4.0-5.0
  Cone 6: 4.5-5.5
  Cone 7: 5.0-6.0
  Cone 8: 5.5-6.5
  Cone 9: 5.7-6.7

Fired Absorption:

  Cone 4: 7.0-9.0%
  Cone 5: 4.0-6.0
  Cone 6: 3.0-4.0
  Cone 7: 2.0-3.0
  Cone 8: 1.5-2.5
  Cone 9: 1.0-2.0

Chemical Analysis

 BaO       0.4
 CaO       0.2
 K2O       2.2
 MgO       0.7
 Na2O      0.1
 TiO2      0.6
 Al2O3    15.8
 P2O5      0.0
 SiO2     72.1
 Fe2O3     1.2
 MnO       0.0
 LOI       6.7%

Plainsman Clays Ltd.
702 Wood Street, Medicine Hat, Alberta T1A 1E9
Phone: 403-527-8535 FAX: 403-527-7508
Email: plainsman@telus.net

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