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The water absorption test can only be used on relatively low fired earthenware, not on vitrified stoneware, which is fired at a much higher temperature. To perform the test one applies a drop of water (or spit) to the unglazed clay surface and then measures the time it takes the drop to penetrate. Objects that are more porous and have larger pore sizes exhibit faster penetration times, other factors being equal. One can also perform the test by thoroughly wetting the object by immersion and then measuring the drying time. In this test objects that are more porous but have relatively smaller pore sizes will take longer to dry completely. Of course, the degree of porosity (i.e., the number and sizes of open internal spaces) has nothing to do with age. It only varies according to clay composition/type, how well the clay was worked (as these affect the mean pore size and size dispersion), and finally, the firing temperature and firing conditions. Proponents of water testing also claim that ancient pottery gives off a more acrid smell then modern pottery as it dries, but this is more likely due to the chemical composition of the clay (i.e., the volatile contaminants) rather than the age of the pottery.
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Re: Water absorption test on old? Chinese pottery - Help needed - Tim - Sep 04, 2015 (08:05 AM)