|Monthly Tech-Tip |
These are the four sieves I used to do a subset of the SIEV test. The label on each shows the size of the opening in microns (the top one, for example, is 425 microns, the next one 297 microns). The process is to wash the clay down through these, dry them and weigh the residue on each. I started with 50 grams of clay and entered double the weight for each one (as if I had processed 100 grams). Consider the second one down, #50: It had 2.6g of residue, that means that 2.6% of the material is finer than 425 microns but coarser than 297. The data yielded by this process produces what is called a PSD or Particle Size Distribution. The total residue on all the sieves is 11.74 grams, that means that 88.26% of the material is finer than the 150 microns (the bottom #100 sieve). Compared to most sedimentary clays, this is quite coarse. In the next step, let's look at what these particles are.
Evaluating a clay's suitability for use in pottery
Would you like to be able to use your own found-clays in your production? Follow me as we evaluate a mystery clay sample provided by a potter who wants to do this.