Use this test to make a rough characterization of materials that are a mix of sand, clay and silt. This test produces numbers that are quick to compare.
Each of these particle types are also chemically, physically and mineralogically distinct from each other.
Characterization of these materials in not firmly set in the ceramics industry as it is in soil science. In soil the size of the grain is most important, but in ceramics the properties of the grains (size, surface chemistry, etc) also determine their type. However for the purposes of this test a generalization is made.
Clays have thin plate-shaped particles held together by electrostatic forces, presenting a cohesive plastic mass when wet. Few clay particles are larger than 5 microns.
Individual grains of silt are approximately the same size in all dimensions and they vary in size across the range between 5 and 60 microns (of course there can be non-clay grains of silt less than 5 microns).
Sand particles are angular, often quartz, but also can be larger particles of any hard mineral. In ceramics the finest size sand that can be seen with the naked eye is about 80 mesh and detected by touch is around 140 mesh (106 microns).
Thus we set the division between silt and clay at 5 microns and between silt and sand at 100 microns. The latter can be measured using standard sieves, the former must be measured using sedimentation of instrumentation.
Silt - Value (V)
Sand - Value (V)
Wikipedia Silt page
USA Standard Sieve Sizes
Test conducted primarily on materials use to make bodies or glazes.
|By Tony Hansen
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