The story of china clay and Cornish stone
18th century pottery manufacturers were constantly trying to unlock the secret of genuine hard-paste porcelain like that imported from China.
Johann Friedrich Bottger, in Meissen, near Dresden in Germany, had discovered the secret in 1709. However, a secret it remained, with workmen reportedly locked inside the factory. Still, the basic ingredients of a very white burning clay and a fluxing material soon became known and English potters began to search for a supply of these.
Apart from the discovery of 'Unaker' clay in the English colonies of North America (Virginia and North Carolina) china clay was not unearthed in Britain until about 1747 when William Cookworthy found a supply near Plymouth in Cornwall.
William Cookworthy's formula
Cookworthy, a chemist, had gone to Plymouth in the hope that he might find the necessary materials for manufacturing the true porcelain. He discovered the two basic ingredients needed - 'Kaolin,' or china clay, and 'petuntze,' or Cornish stone. Both are made up of partially decomposed granite. In 1768 he patented his formula and established a new factory in Plymouth to make hard paste porcelain.
The enterprise was short lived and although the patent passed to Richard Champion, who attempted to renew it in 1775, hard paste porcelain has never been successfully manufactured in Britain except at Royal Worcester Porcelain. It is still used there today for the manufacture of ovenproof ware and laboratory porcelain.
The real importance of William Cookworthy to the English pottery industry was his discovery of china clay and Cornish stone. Josiah Wedgwood (before Cookworthy's patent of 1768) had already experimented with 'Unaker' and was certainly using the material in his improved creamware.
When Champion attempted to renew the patent, Wedgwood gathered many potters to support him in opposing it. By Act of Parliament the patent formula for hard-paste porcelain was upheld, but the use of china clay and Cornish stone was exempted for the purposes of manufacture of any other ceramic substance.
The New Hall Porcelain Company
The cost of this legal battle crippled Champion who passed his formula over to a group of Staffordshire potters known as the New Hall Porcelain Company, which continued to manufacture the ware until 1810 when it gave way to the manufacture of bone china.
In addition, however, New Hall acted as agents and distributors of the materials. They supplied Staffordshire potters who had not taken out their own leases on Cornish mines.
Meanwhile, the larger pottery manufacturers formed consortia to operate their own china clay pits.
