Pottery and Porcelain

We can only marvel that such porcelain as, say, that of the Ming Dynasty (1368-1643), with all the technique involved in the selection of materials and its treatment, the craftsmanship, colouring and glazing, was produced before science, as we now use the term, had any voice in such matters. The 

Chinese hard paste porcelain consisted of kaolin in a pure and very finely divided state, and petuntze (finely ground felspathic stone) and the glaze was made from selected petuntze mixed with specially prepared lime. 

For supplies of porcelain for laboratory purposes this country has hitherto been mainly dependent, as in the case of glass, on Germany. Our chemists have taken the matter in hand, however, and remarkable progress has been made by several British manufacturers. Research on the subject of. hard porcelain is progressing, and there is good ground for hoping that this branch of the industry will be retained here in the future. 

The danger to workers of lead oxide as a constituent of glazes for earthenware has also provided a problem for chemists. The employment of lead silicates instead of oxide, as suggested by Thorpe and Sim-monds, is less harmful and the lead glazes have been largely superseded in recent years by mixtures containing silica, alumina, potash, and soda, with about 10 per cent, of boric acid to increase the fusibility. Where lead is an essential constituent it is applied in the form of silicate. 

In our second chapter we li ve dealt with the heavy chemicals and alkalies, and we will proceed now to consider the production of other chemical substances of value in industry, or useful for domestic, medicinal, scientific, or other purposes. The importance of this branch is so wide and fundamental that it is not too much to say that industry as a whole is largely dependent on an adequate supply of chemical proclucts. The field is so great that we cannot attempt to indicate all or nearly all the substances coming under this head, but we will choose a few examples of different types, all rendered available by scientific methods. 

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For many centuries cobalt was used to color glass, pottery, and porcelain and as an enamel. It is also used as a dye and paint pigment. 

Cadmium acetate is used in the pottery and porcelain industry for producing iridescent effects the borotungstate forms an aqueous solution of high density when concentrated (d = 3.28), useful in die mechanical separation of minerals and in density gradient techniques the bromide, like the zinc salt, is used in photography, process engraving and lithography. 

FIGURE 1.12 Woodblock prints of the stamping of a pattern on the surface of a bowl (a) and the firing of a dragon kiln with several chambers (b). These kilns were so named because they snaked their way at a constant gradient up the contours of a hillside. Taken from T ien Kun K ai Wu, 1637 print from Description of Chinese Pottery and Porcelain [9]. 

Bushell, S. W., Description of Chinese Pottery and Porcelain (translation of "Tao Shuo ). Oxford Univ. Press, Oxford, 1977. 

Hobson, R L., Chinese Pottery and Porcelain. Dover, New York, 1976. 

Ji) Prepare a short account of the manufacture of pottery and porcelain. 

L. Jiazhi, The evolution of Chinese pottery and porcelain technology, in Ancient Technology to Modem Science, Ceramics and Civilization, Vol. 1, W.D. Kingery (ed.), The American Ceramic Society, Columbus, OH, 1984, pp. 135-162. 

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