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ABOUT TYPES OF CLAY SOIL


QUESTION

How different types of clays, contribute differently to ceramic making





According to Shepard (1982:6), Clays is fine grained earthly material that develop plasticity when it is mixed with water, in that matter when clay its plastic it can be form or shaped, also clay can be defined as slippery soil and also stricky. But also clay can be define as particular group of minerals, a category of rocks and soils in which those minerals predominate and specific particle size grade that constitutes the major fraction of those minerals, rocks and soils. Clay is also one of the forms of soil, it has a smallest particle among the other forms and has good water storage, clay is typit to touch but smooth when dry. Clay has got white colour that means the original colour of clay is white but other colour are due to organic matter such as iron and carbon when mixed. When clay is dry it cracks because it shrink, the finest part of clay called colloid. Now I provide the types of clays contribute differently to ceramic making as follows;

Kaolin Clays, this is very pure inform, also a standard clay to compare other clays it is always white especially milky white and when it used to make ceramics for vessels it should be very fine and temperature required is high 13500C when clay resist fire is refractory, it has low plasticity, Kaolin also used to decorate or for decoration, they are usually residual kaolinites that are high in alumina over 30% of their composition in most cases and low alkali impurities which act as fluxes, lowering the melting and vetrification point (Rice 1987:51).

Ball clays are important in the manufacture of white wares, which include China tableware, tails and sanitary ware, these clays are composed principally of the clay mineral kaolinite, although some may contain smectites and illites, ball clays usually have 40% to 60% silica and 30% alumina. In addition, they include significant amounts 5% or more organic material and soluble salt, ball clay are very fine textured, highly plastic. Ball clays due to presence of organic material and changed is colour to become organic acid were responsible and it is fired in high temperature (Rice, 1987:51).

Stoneware Clays, is similar to porcelain Koilein but it affected by impurities for example iron, calcium and feldspar, the maturity of this clay is 13000C, stoneware clays contribute to ceramic making. (Shepard, 1982)

Fire clay, as it as name fire, high firing temperature is used about 1500-17000C it used some vehicle and its common used to insulate bricks, it characterized with high plasticity and high Refractory. (Shepard, 1982).

Earthenware clays, it is all around, it has got high percentage of iron oxide, it makes the clay of low firing temperature iron oxide is a flax is to breakups, it fired at 11500C temperature which is very low. (Rice, 1987).

Slip clays, suspension of clay in water or pourage of clays, clays particles in water, slury heaver liquid of clays used as glaze to decorate. (Shepard, 1982).

Therefore, different types of clays contribute differently to ceramic making whereby the geological field study of clay deposits gives some idea of their general mode of formation, their homogeneity, impurities and texture, the determination of clay mineral composition gives more specific data which have direct applications because the different species of clay vary greatly in their physical properties and firing behaviour.





REFERENCES

Shepard G. (1982). Ceramics for Archeologist. Washington DC, Carnigie

Prudence M. Rice (1987). Pottery Analysis: A Sourcebook the University of Chicago, London

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