Dry strength relates to the ability of maintaining the current form of ceramic objects undergo a drying process so as to dry the ceramic object is strong enough for the next process. This is very important because the nature of the ceramic body must be strong enough to be lifted, refined, and are arranged in a furnace. Clay has high plasticity will be higher the dry strength. Ballclay is a material that has good dry strength, but when made objects will arise cracked.
Dry strength is affected:
1) The fineness of grain
2) the plasticity
3) curing time (aging)
4) the amount of water forming
5) mixing with other materials
6) formation technique
Figure 30. ceramic objects through the drying stage
Colour Fuel
The color of the clay is one of the physical characteristics that can be seen langsung.Warna is caused by impurities (impurity) that are organic and clay anorganik.Tanah in a raw state obtained from the place of origin (deposit) has a variety of colors such as beige, yellow, brown, red brown, gray, and hitam.Perbedaan color is affected by the comparison levels ingredients include a mixture of clay or dirt humus (organic), iron oxide (Fe), and others.
After experiencing the process of burning clay color will appear which is sometimes different from the colors in a raw state, it is influenced by a substance / material contained therein are chemically bonded. Dirt organic nature will be burnt during the combustion process takes place, while the material is chemically bound will cause the clay to color.
Figure 31. The color of clay Different
Clay color caused by substances that mengotorinya.Warna gray to black containing carbon and plant debris, while the red color containing iron oxides (Fe) .Warna can also be caused by a mixture of other oxides as pigments such as cobalt (Co) , copper / cupper (Cu), chromium (Cr), iron (Fe), manganese (Mn). In general, the type most widely Earthenware clay containing iron oxides (Fe) .Here are grilled biscuit color samples (temperature 900 ° C) pure clay Sukabumi, Pacitan, Malang, Bojonegoro, and Singkawang as shown in the figure below.
Figure 32. The difference in the color of the clay after baked biscuits temperature of 900 ° C