Porosity Test – When considering the suitability of your clay for a particular use (coffee mugs, flowerpots, sculpture or decorative wall tiles), shrinkage and absorption are factors which will impact.
Simple way is to weight a unglazed fired clay sample, then soak in water. After overnight, the sample is wiped off excess water then weight again. The increase after soaking will be the percentage of porosity of the clay body.
In general, the porosity of fired clay bodies directly connected to their mature temperature. Earthenware in 4-10%, stoneware in 1-6%, porcelain in 0-3%.