A clay that has negative shrinkage during the glaze firing

Thursday 27th October 2016

It seems impossible but that is what happens with this one at cone 03. This is a native material that was found on the banks of the South Saskatchewan river near Hayes, Alberta (and brought to me for testing). Even when fired to maturity (around cone 2) it still has 10% porosity! This specific sample has even been ball milled for hours and it still does not shrink. And it still feels sandy on the potters wheel. It also has incredible dry strength, the highest I have ever seen. Yet its drying shrinkage is still less than 7% (that of a typical plastic pottery clay). Plus it has very high plasticity. This behavior defies logic, I have found a good explanation.

Pages that reference this post in the Digitalfire Reference Database:

SHAB Shrinkage/Absorption Test, Firing Shrinkage, Porosity

This post is one of thousands found in the Digitalfire Reference Database. Most are part of a timeline maintained by Tony Hansen. You can search that timeline on the home page of digitalfire.com.