... of the organic matter is up to 15%. It’s main chemical composition are SiO2, Al2O3, H2O, C, H2 and a small amount ... of Fe2O3, TiO2, Na2O, K2O.The colour is various and mostly are black and gray.As it content deferent impurity,it became white ... ,after roasted.The under ball clay are high in plasticity, strength,viscosity and bonding nature. It is one of the important combination clay ...