This is a Hawthorne Fireclay sample from 1997, these test bars are made to measure fired shrinkage and porosity. Top bar: Cone 10R. Proceeding down from there is cone 11, 10, 8, etc (oxidation). Drying shrinkage is 4.5%. Firing shrinkage is about 8% at cone 11 going down to 7% at cone 6, it is thus very stable across a wide range. Porosity is likewise, 3% at cone 11 slowly rising to 5% by cone 6. So this material is already fairly vitreous by cone 6 yet still stable at cone 11.