The process of casting came into use about 1730, and the carving of these moulds (in alabaster first, from which the “pitcher” mould could be made), became the most critical operation of all the potter’s work. This work required all the skill and artistic instinct of the carver and of the designer. Block-cutters, as they were called, became famous. The best known were the two brothers, Aaron and Ralph Wood of Burslem. Aaron Wood (1717-85) was bound apprentice in 1731 to Dr Thomas Wedgwood, some of whose best models he is supposed to have made.[52] He afterwards worked for J. Mitchell, of Burslem,[53] and for Wheildon of Fenton, acquiring such a reputation that he was allowed to work in a locked room, that his art might thereby be kept secret. CHAPTER V. THE BEGINNING OF THE FACTORY. The industry was entering on a new phase. The introduction of moulds had required specialized block-cutters, flat and hollow-ware pressers and casters. And the specializing in the mixtures of the clay body lead to further changes. Till 1740 the same clay body served for both salt glaze and lead glaze, but about this time manufacturers began to specialize in either salt _or_ lead glaze, and to use different bodies and mixtures to suit the varied glazes. And, just as they had to arrange to import clays, so they had also to arrange to export their wares. A London agent, a Liverpool agent, perhaps a Birmingham agent became necessary. This sort of business could no longer be carried on by a master potter on sixteen shillings a week. The master potter became a capitalist. No business could be successfully carried on with a turnover of one ovenful a week. The first attempt to increase the output was made by either one Shrigley, of Burslem Hadderidge,[54] or by John Mitchell of the Hill Top.[55] As no potter, so goes the story, had ever had more than one oven, their inventive faculty went no farther than to construct a larger oven than usual. The pioneer, whoever he was, built a new one so large that it collapsed, to the great joy of his conservative rivals. Soon afterwards, however, the Baddeleys, said to have been the sons of a Moddershall flint-grinder, put up behind their factory at Shelton a row of no fewer than four ovens; and about 1743, Thomas and John Wedgwood, known as “of the Big House,” built a tiled factory with five ovens.[56]