Home | Products | Overview
H440 has a fairly high drying shrinkage and thus care and attention during drying are necessary for larger pieces, especially flat plates, shallow bowls, and sculptural ware. Cover pieces to make sure they dry evenly, take extra time drying if needed, and start the kiln very slowly (candle overnight) for final water expulsion.
H440 is a deep red firing iron reduction body. The significant Firered native clay complement in its recipe is the reason for the attractive color. Like other bodies of this type, H440 has been formulated so that cone 10R is at its transition point from a light brown to a dark red brown. When fired just right the surface is a patchy network of darker vitrified areas beginning to invade the lighter colored matrix. If over-fired or over-reduced the surface will burn a dark solid red brown. Good color is possible as low as cone 8 reduction.
H440 contains significant amounts of iron stone concretion particles which melt vigorously in high temperature reduction and which blossom on the base surface and bleed up through glazes. The degree to which these speckles melt and develop is dependent on the degree of reduction.
H440 can be fired in oxidation, but its color is much lighter; a leather greenish tan with a very fine speckle. It will tend to blister and bloat sooner in oxidation (i.e. cone 11) because the coarser particles in the clay are much more active in producing gaseous by-products during decomposition.
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. Also, strength can be significantly impacted if glazes do not fit. Use an ice water:boiling water immersion test to make sure.
H440 bisque ware is quite dense with channels formed by larger particles. This means that glazes can pinhole during drying as water-displaced air escapes from larger-than-normal surface holes that channel air out from inside.
Drying Shrinkage: 6.0-7.0% Dry Strength: n/a Water Content: 20.0-21.0% Drying Factor: C120 Dry Density: n/a
+48: 0.0-0.5% 48-65: 1.0-3.0 65-100: 4.0-6.0 100-150: 2.5-5.0 150-200: 4.0-7.0 200-325: 6.0-10.0
Cone 8: 4.5-5.5% Cone 10: 5.0-6.0 Cone 10R: 5.0-6.0
Cone 8: 4.0-6.0% Cone 10: 3.0-4.0 Cone 10R: 2.5-3.5
BaO 0.5 CaO 0.4 K2O 1.7 MgO 0.5 Na2O 0.1 TiO2 0.7 Al2O3 16.4 P2O5 0.1 SiO2 68.0 Fe2O3 3.1 MnO 0.0 LOI 8.4%
|Plainsman Clays Ltd.
702 Wood Street, Medicine Hat, Alberta T1A 1E9
Phone: 403-527-8535 FAX: 403-527-7508