|Monthly Tech-Tip |
Here is how the pugmill operators at Plainsman Clays gauge the stiffness of the clay coming out of the pugmill. The machined nylon roller is on a slant and weighted. The softer the clay the more lines show. When they are like this (5th line steady) the operator knows the water content is around 22% for this clay, Polar Ice. For each type of clays it is different. Stiffness at pugging must also compensate when the clay tends to stiffen or soften over time. Over the years they have tried many devices to measure stiffness, but this has proven the most reliable.
In ceramics, clays exhibit plasticity in accordance with their recipe but also the water content. The stiffness considered correct varies for different types of forming methods.
The practice of removing air from clay as it is pugged. Deaired clay has better forming properties and produces a smoother fired surface.