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. It 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 be used in casting slips.
Midstone-based bodies offer these advantages:
Midstone fired bars (cone 10R, 10, 8, 7 and 6 oxidation). Although the cone 10R test bar appears stable, we do not recommend using Midstone pure at cone 10R, it is too vitreous and could bloat. It needs ball clay anyway (for plasticity) and ball clay is refractory (so this combination will be suitable at cone 10R).
Midstone burns to a light straw color at cone 5, progresses to a solid light grey-buff at cone 7-8 and grey in reduction.
Bodies made from Midstone are easy to fit glazes to (because it has a high natural quartz content). Ones that craze on porcelain will likely fit Midstone.
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.
Drying Shrinkage: 5.8-6.8% Drying Factor: C120
Sieve Analysis (Tyler mesh):
48-65: 0.25-1.0% 65-100: 2.0-4.0 100-150: 2.0-3.5 150-200: 5.0-8.0
Cone 6: 4.5-5.5% Cone 8: 5.0-6.0 Cone 9: 5.5-6.5
6: 3.5-4.5 Cone 8: 2.0-3.0 Cone 10: 0.5-1.5
BaO 0.4 CaO 0.2 K2O 2.0 MgO 0.8 Na2O 0.1 TiO2 0.6 Al2O3 18.2 P2O5 0.0 SiO2 68.2 Fe2O3 1.4 MnO 0.0 LOI 8.0%
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|Plainsman Clays Ltd.|
702 Wood Street, Medicine Hat, Alberta T1A 1E9
Phone: 403-527-8535 FAX:403-527-7508