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The granite moors of Cornwall and Devon were formed about 300 million years ago and contained 3 main minerals, felspar, quartz and mica. In some areas the white felspar decomposed to a soft white material, known as kaolinite - the main ingredient of china clay. China clay is extremely fine and is formed by a unique combination of climatic and geological conditions. The coarsest grains of china clay are finer than most talcum powders. In 1768 William Cookworthy, a chemist based in Plymouth, took out a patent for the manufacture of a 'kind of porcelain newly invented by me, composed of moor-stone or growan and growan clay'. It was the result of some 20 years of research. Cookworthy had studied the theoretical knowledge of methods and materials used in hard porcelain manufacture in China and, like others at this time in Europe, had been searching for a source of suitable materials in his home country. The industry flourished and the rate of production rose sharply during the 19th century as china clay began to be employed in the production of paper, as a filler. The uses for china clay continued to extend and today china clay provides the gloss in high quality papers, is used in paints, products made of rubber, in plastics, cosmetics, pharmaceuticals and more, in addition to its suitability for making high quality ceramics such as porcelain and bone china. In the earliest times of its production, clay was removed from the ground with hand tools and taken to an area where it was worked with a diverted stream of water. The milky suspension produced by clay and sand was left so that the coarse sand settled and could be separated. The clay was placed in settling pits then allowed to thicken, drying in open air. Later production became more efficient, speeding up the drying time. Long buildings with heated floors were built to dry the clay. Since the 19th century clay has been removed by high pressure hoses, washing it from the sides of the pit. Production methods today are highly mechanised and computer controlled. You can visit the china clay museum at Wheal Martyn to find out more about the development of the clay industry. |