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  1. I'm working with a clay that has a tendency to flop with little warning. From what little I know this can be a problem with plastic clay bodies holding more water than more forgiving, less plastic bodies. So with this in mind I'm looking at making adjustments but I'm getting conflicting information on what some accepted water content values are. Plainsman P700 has a % water of 23.5 - 24.5 Plainsman describes P700 as "our most vitreous cone 10 white body, it is the closest thing we have to a true translucent porcelain body. It is a mix of 50% Grolleg kaolin with feldspar and silica. We also add micro-fine bentonite to improve its plasticity." In the Febreuary Ceramics Monthly (thanks Tom) the water contents are significantly higher than the figures from Plainsman. I'm wondering are clays so different in the Unites States? I'm curious because the clay I'm working with holds aproximately 26% and is mixed up as a high fire, buff, stoneware. It works well for the most part. Fires to an 11 with no issues and kitchen tested absorption showed it was near zero at cone 10. But it doesn't stand up as well as the commercial Plainsman clays and I want to know why. thoughts much appreciated 20 epk 20 OM-4 ball clay 20 silica 20 custer potash feldspar 12 hawthorn Bond Clay 8 pv clay Percentage Analysis by weight 71.13 % SiO2 23.24 % Al2O3 3.06 % K2O 0.73 % Na2O 0.28 % CaO 0.32 % MgO 0.59 % Fe2O3 0.05 % P2O5 0.59 % TiO2
  2. Introduction of SAS Formulation - hypothesis The industry standard has been formulation based on particle size distribution (PSD), which includes density packing. The Zameck article proposed formulation based on the PSD principle; which included emphasis on density packing. However, particle size is a measurement that only determines the plane (face) of a particle, but does not include the depth. A sugar cube represents a perfectly square particle: which has the same plane and depth equal. Clays however can have the same particle size on the face, but vary widely in depth. So a large grain of clay could be represented by a sugar cube shape: but in reality the depth can be anywhere from a thickness of hair up to a normal sugar cube shape. So using PSD as a determining factor for packing density is inaccurate; because it does not include the measurement of depth (platelet.) Specific Area Surface (SAS) is:Specific surface area (SAS) is a property of solids defined as the total surface area of a material per unit of mass. The SSA can be simply calculated from a particle size distribution, making some assumption about the particle shape. The SAS is far more accurate, in that it takes into account both the width (particle size) and the depth (platelet size) of clay. In common calculations: a potter will factor in a 200 mesh clay: but has no idea if that platelet size is 20-50-100-1200 mesh thick. So determining packing density solely on the basis of particle size is inaccurate, because platelet size is not factored. A 200 mesh clay could have a SAS as low as 18, and as high as 28: which this variance alone confirms the inaccuracy of using particle size alone. In addition to using the SAS in determining accurate grain size; the SAS will also give the potter insight into the plasticity of the clay of choice. The higher the SAS goes, the more plastic the clay will be. (Applicable to ball clays and bentones primarily). More importantly, the SAS becomes the basis of formulation because it factors total grain size. So from here, the SAS formulation needs to be applied.. Nerd
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