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H435

High fire, moderately sandy, plastic, semi-vitreous, grey burning lightly speckled, general purpose native material body for reduction fired stoneware.

H435 has been manufactured for many years. It has about 15% fine sand and is quite high in silty stoneware clay; these are balanced by our native plastic stonewares and some of our high coal, super-plastic ball clay. H435 is semi-vitreous and has been used by people who want a compromise between the properties of H431 and H550.

Process Properties

H435 contains significant amounts silty clay and sand which give it a lower drying shrinkage and considerable texture during throwing. It has a feel that is somewhere between the smoother H550 and the coarser H431. H435 contains a high coal ball clay which imparts a dark grey blackish color to the pugged. This ball clay significantly masks the feel of the sand during the throwing process.

The open structure of H435 also means that extra water can be absorbed during throwing making it more susceptible to water-splitting (the sand provides openings into which water can penetrate). Thus it is beneficial to use water sparingly during throwing and make sure that it does not stay long on points where the clay is under stress (i.e. the outside of the belly on a vase). Since H435 generates slip during throwing, try to develop a technique where the slip produced during centering can be employed later as a lubricant during throwing.

Firing

H435 fires to a variegated speckled stone-grey color at cone 10R. It does not have as much speckle as H431 and has more than H550. In oxidation firing there is some very fine specks and the body retains a stoney light grey color through the cone 9-11 range. Although H435 may appear stable at cone 11 sometimes we cannot guarantee successful results in this range.

Glazing

Although it has a low overall thermal expansion H435 is easy to adapt non-crazing glazes to. It contains plenty of high quartz plastic clays. Thus a glaze which crazes on a porcelain body will usually fit well on H435. It is still possible to get crazing with glazes high in sodium and potassium or very low in silica or alumina. Thus you should watch out for high feldspar low flint/kaolin glazes (these are quite common). Please contact Plainsman if you need help to adjust your glazes.

H435 is quite dense in the bisque state compared to porcelains, thus it does not absorb water as fast or evenly. This may lead to some pinholes after the glaze has dried but these are no cause for concern as they heal during normal firing. We suggest that you do not bisque this body any lower than cone 06 because it does contain some carbonaceous material that needs to be burned away before the glaze firing if possible.

Glaze Recipes

You can develop a compatible glossy or matte base for this body from our suggested starting point base recipes available on our Internet web site at http://digitalfire.com/education/glaze/cone10.htm. Information is given on how to fit the glaze to your body and how to customize it it for colors, opacity, speck, variegation, etc. For slip decoration, be careful to match drying and fired shrinkage of the slip with the body since low temperatures generate little glass to adhere the slip.

Thermal Expansion

This chart was derived from a specimen fired once to cone 10 reduction in the Plainsman lab and tested in an Orton dilatometer. 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: 5.3

Physical Properties

 Drying Shrinkage: 5.5-6.5%
 Dry Strength: n/a
 Water Content: 19.5-20.5%
 Drying Factor: c120-
 Dry Density: n/a

Sieve Analysis (Tyler mesh):

     +48: 0-0.5%
   48-65: 1.5-3.5
  65-100: 5.0-10.0
 100-150: 3.0-6.0
 150-200: 7.0-11.0
 200-325: 8.0-12.0

Fired Shrinkage:

   Cone 6: 4.0-5.0%
   Cone 8: 4.5-5.5
  Cone 10: 4.5-5.5
 Cone 10R: 5.0-6.0

Fired Absorption:

   Cone 8: 4.0-5.0%
  Cone 10: 2.5-3.5
 Cone 10R: 1.5-2.5

Chemical Analysis

 BaO       0.5
 CaO       0.2
 K2O       2.1
 MgO       0.5
 Na2O      0.1
 TiO2      0.6
 Al2O3    16.9
 P2O5      0.0
 SiO2     69.8
 Fe2O3     1.2
 MnO       0.0
 LOI       7.9%

Plainsman Clays Ltd.
Box 1266, 702 Wood Street, Medicine Hat, Alberta T1A 7M9
Phone: 403-527-8535 FAX: 403-527-7508

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