|Monthly Tech-Tip |
While a PCE test is certainly desirable, few people or companies have the ability to do this test. But the much-more-accessable SHAB test produces physical testing data that is perhaps even better. The last column of numbers (titled "ABS", for absorption) prove that the clay on the right, my code number L4380, is very refractory. Even at cone 10R it has 11.3% absorption, and its firing shrinkage is only 3.9%. How do I know cone 10 11.3% porosity is impressive for a fireclay? Because I have tested many other fireclays using this same procedure. What about the clay on the left, L4378? In comparison, its cone 10R porosity of 6.4%, making it quite a bit more vitreous. But not enough to qualify it as a stoneware (which would have 1-2% absorption and 6-7% firing shrinkage). Additionally, many common fireclays also exhibit same level of maturity as L4378. So is it a fireclay or a stoneware? A 10% feldspar addition would convert it to stoneware, so there is merit in calling it a "stoneware material". But that is "in comparison to" the very refractory L4380. But, if we were compare L4378 to any of the false fireclays commonly sold, then it could certainly be termed a fireclay in comparison.
In the ceramics industry, clays that are resistant to deforming and melting at high temperatures are called fireclays. Kiln bricks are often made from fireclay.