two principal materials used to make porcelain, china clay and Chinese pottery stone. After many years of travel and research William Cookworthy determined that Cornish china stone could be made to serve as equivalents to the Chinese materials and in 1768 he founded a works at Plymouth for the production of a porcelain similar to the Chinese from these native materials. In 1768 Cookworthy took out a patent for the exploitation of these Cornish materials in the manufacture of porcelain. The company began with 14 shares of £15 or £20 each, three held by Cookworthy, and the others one each by a group of his relatives and "prominent Bristol men", including Richard Champion of Bristol. More capital was needed later, and the company seems to have been loss-making. Thomas Pitt, 1st Baron Camelford, who owned the Cornish lands where the materials were sourced, took an interest in the company, whose success was naturally in his interest. The wares of Plymouth and the first years at Bristol are not easily distinguished, and many prefer to classify pieces as "Cookworthy" or "Champion". Bristol The factory was removed to Bristol in 1770 and was afterwards transferred to Richard Champion, a merchant already a shareholder. The patent was sold to Champion in 1773. An application to extend it was opposed by Wedgwood and other pottery companies, and mostly refused, so it expired in 1782 at the end of the original term, though Champion was granted rights for 14 years for the use of Cornish materials to make translucent porcelain. In the end he sold his rights in 1781 to the Staffordshire company that started New Hall porcelain in 1782, including New Hall. In the end the English invention of bone china was to prove the most satisfactory material, and the great majority of English porcelain had moved to that by 1820. Marks Factory marks are of only limited help, as many pieces are unmarked, and the main mark was also used at Bristol; this was in underglaze blue, the alchemical symbol for tin, also used for the planet Jupiter. This presumably referred to Cornwall's main mining product. Other marks, such as a "B", were only used at Bristol. Notes References Honey, W.B., Old English Porcelain: A Handbook for Collectors, 1977, 3rd edn. revised by Franklin A. Barrett, Faber and Faber, British porcelain Devonian pottery Ceramics manufacturers of England Plymouth, Devon History of Devon