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H443

Description

High temperature, slightly textured, plastic, semi-vitreous, iron-brown speckled, general purpose, native body for dark iron reduction fired stoneware.

H443 is a classic mottled-brown reduction speckled stoneware. Unlike H440, it generally fires with no red hues. H443 is not a vitreous body, it stops short of complete maturity to retain interesting color. It is best suited for decorative pieces large or small (vases, bowls, planters, etc.). Its fired strength does not make it ideal for use in functional ware, however H443 has been used for this very purpose by hobbyists, educational institutions, professional potters, and small manufacturers for many years. This has been done mainly for its compelling color and for its robust drying properties and excellent green strength.

Process Properties

H443 is a reddish brown in pugged form and made totally from a blend of Plainsman native stoneware materials. It has good plasticity (exellent if it is stiffer) and exhibits only a slight sandy texture during throwing (by virtue of kaolinized sand in its recipe). H443 has an excellent distribution of clay particle sizes in the plus 325 mesh range and these are a factor in its fast drying and high dry density and strength. However, even though H443 dries well it does have a fairly high drying shrinkage and thus care and attention are necessary to be sure larger pieces, especially flat plates, shallow bowls, and sculptural ware are dried evenly.

Firing

These test bars (left to to right) compare H440 and H443 at cone 10R (top) and cone 10, 8 and 8 oxidation.

H443, like other iron reduction bodies, depends on stopping short of being vitrified to achieve the characteristic warm brown coloration. H443 has been formulated so that cone 10R is at its transition point from a toasty brown to a dark brown. When fired just right the surface is a patchy network of darker brown vitrified areas beginning to invade the lighter colored matrix. If over-fired or over-reduced the surface will burn a dark solid brown. If you wish to fire at a lower reduction temperatures, good color is possible as low as cone 8.

H443 contains some iron stone concretion particles that melt vigorously in high temperature reduction and blossom on the bare clay or bleed up through glazes. The degree to which these speckles melt and develop is dependent on the amount of reduction imposed.

H443 can be fired in oxidation, but its color is dramatically lighter (a leather to greenish brown from cone 6 to 10) and the speckle is much finer. If overfired H443 will tend to blister and bloat sooner in oxidation because the coarser particles in the clay are much more active in producing gaseous by-products during decomposition.

If you are producing functional ware and glazing the entire surface, you might like to consider using a stronger buff burning stoneware instead.

Glazing

Since H443 is a dark stoneware it readily bleeds its iron into glazes and colors and significantly colors them. This will especially be the case in reduction firing, brightly colored glazes will not be as vivid as they would be if used on porcelain. On the other hand, this effect will enhance the appearance of earthtone and variegated glazes.

H440 has a reasonably high porosity so the fired body will tend to absorb water. Thus it is important that glazes not be crazed to assure that ware is water tight and will not be susceptible to moisture expansion. Strength can be significantly impacted if glazes do not fit properly (use an ice water:boiling water immersion test to make sure).

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, Ravenscrag.com and AlbertaSlip.com). For slip decoration, be careful to match drying and fired shrinkage of the slip with the body.

Physical Properties

 Drying Shrinkage: 6.0-6.8%
 Dry Strength: n/a
 Water Content: 20.5-21.5%
 Drying Factor: C120
 LOI: 6.5-7.5
 Dry Density: n/a

Sieve Analysis (Tyler mesh):

     +48: 0.0-0.5%
   48-65: 1.0-3.0
  65-100: 5.0-7.0
 100-150: 3.0-5.0
 150-200: 4.0-7.0
 200-325: 7.0-10.0

Fired Shrinkage:

   Cone 8: 5.2-6.2%
  Cone 10: 5.5-6.5
 Cone 10R: 5.5-6.5

Fired Absorption:

   Cone 8: 4.5-6.0%
  Cone 10: 3.0-4.0
 Cone 10R: 2.5-3.5

Chemical Analysis

 BaO       0.5
 CaO       0.4
 K2O       1.6
 MgO       0.5
 Na2O      0.2
 TiO2      0.8
 Al2O3    18.9
 P2O5      0.0
 SiO2     66.1
 Fe2O3     2.5
 MnO       0.0
 LOI       8.6%

Gallery

A cone 10R planter made from H443. In this firing it has a reddish tone (the color varies according to reduction). 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