Clay Shrinkage
All clays shrink during drying. Generally the amount of drying shrinkage is related to plasticity, the more plastic a clay the more it dries (and likely the more prone it will be to drying cracks). Drying shrinkage is also related to particle size, the smaller the ultimate particle size the more the shrinkage. Drying shrinkage determination on a clay is an easy test that can enable you to effectively compare it with other clay materials (for plasticity and particle size). Of course, to get consistent results on the same material requires the same water content. Some clays shrink so much and dry so slowly that it is not practical to make bars of the pure material (e.g. bentonite, ball clay). In these cases silica is mixed with the specimen (e.g. 50:50) or it is blending with a calcined version of itself.
Fired shrinkage (shrinkage from dry to fired) is an indicator of degree of vitrification. As a clay is fired higher it shrinks more and more until a point of maximum shrinkage (after which swelling occurs as a precursor to melting). If fired shrinkages are measured over a range of temperatures for a body it is possible to create a graph to get a visual representation of the body's maturing range. The shrinkage plotted against temperature produces a line that increases to a maximum, levels out then drops off.
Out Bound Links
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In Bound Links
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