The nature of the clay shaft is ceramic body’s ability to absorb water, or can be said as well as the degree of density ceramic body weight after being burned. Porosity properties is very important because of the presence of this nature will allow the evaporation of water or water-forming membranes out during the drying process and combustion. In the process of this nature pengglasiran also affect the absorption of glaze on a ceramic object that will have the sticking power before the glaze firing process implemented.
Figure 27. Jars must be watertight
Porosity greatly influenced by the nature of the coarse and the fine particles of clay that form the body keramik.Tanah clay containing soil-forming particles consisting of fine particles and coarse particles. Comparison and large grains in the soil greatly affect the properties of the soil. Flexible clay generally contains particles finer so that the shrinkage of dry and shrinkage of fuel will be high and this also affects the porosity, clay plastic tend to possess porosity low, sebailknya clay less plastic shrinkage dry and shrinkage fuel low so porositasnya high.
Clay must be quite shaft, in order:
1) Water plastic (formation water) that amount of water is added to clay to be formed) can evaporate easily during the drying process, resulting in dry shrinkage.
2) Water chemistry (water chemically bound) that the water contained in the clay naturally could easily be out at the beginning of the combustion process, thus avoiding and eruptions of steam and cracked.
3) Various gases arising from the combustion process Zatzat existing organic soil can come out, during the combustion process occurs again called shrinkage shrinkage fuel.
Figure 28. ceramic shaft Agency (seen with an electron microscope)
Combustion temperature greatly affect the porosity and strength of baked clay, but when the combustion temperature is continuously raised, there will be a process penggelasan on clay and strength to be reduced. This is as shown in the following figure.
Figure 29. Effect of fuel temperature on the porosity and strength of clay