These two clays arrived for testing and characterization today. They have lumps up to 1 inch. After making sure the material is completely dry I spread out about 1kg on the concrete floor and then roll it using a large rolling pin. This effectively breaks the lumps. If I just keep rolling the whole mass thins more and more and the lumps get smaller and smaller (making them much easier to slake). Another benefit is that rocks are located, since the rolling pin is unable to break them. Finally, the homogeneity of the material is clearly visible. In these two clays it is clear that the left one is homogeneous, all of the lumps being the same grey material (the right one is looking more like over burden than clay, likely not worthy of further investigation).
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.
Case Study: Testing a Native Clay Using Insight-Live.com