Shape clay particles as small plates that resemble the shape of a hexagon (hexagonal) with a flat surface, but can not be seen with the eye in the form of particles such langsung.Dengan This causes the clay have the nature of clay (plastic) and malleable when mixed with water. Halini because the particles are mutually slid to one another with water as a lubricant.
Figure 35. The shape of clay particles.
Theoretical formula is Si2Al2O5 (OH) 4 or Al2O3.2SiO2.2H2O (Velde, 1992).
Figure 36. (a) Structure sheet kaolinite (b) particles of clay
Comparison of major grain and granular clay particles will have an effect on plasticity, dry strength, shrinkage, porosity, and the character of the objects after being burned. Clay structure;
a. The fine structure (plastic): clay
b. Rough structure (not plastic): sand
Comparison of clay (clay), soil sediment (silt) and sand (sand) can be seen in the image below.
Figure 37. Comparison between clay, soil sediment, and sand
The sand has a size of between 0.05 to 2 mm, soil sediment diameter from 0.05 to 0.002 mm, while the clay (clay) having a particle size of less than 0.002 mm. From the above description, the clay has properties different both from the nature of plasticity, workability, susutnya, fuel temperature, porosity, and color fuel light / dark. In order to meet the requirements to be used it is necessary to repair the soil properties are thus performed before the forming process.
Keep in mind that the addition of each ingredient will affect the properties of the clay. The materials that can be added to improve the character of clay:
1) As a plastic material or bentonite adalahballclay
2) As a material hardener / filler is flint, grog / chamotte, sand, talc
3) As a material melting / flux is feldspar, lime, magnesia, dolomite and iron oxide.