In fact all that was wanted to convert the peasant pottery of North Staffordshire into a great business was the stimulus given by the refined hand of Elers, and the new demand in the new clubs and coffee houses. When once improvements in manufacture began, invention followed invention; and though the records during the second quarter of the eighteenth century are full of entries of patents, registered for the performance of every possible and impossible pottery process, yet most of the improvements—especially the vital changes in body and glaze made by Astbury and Booth—became public property unchecked by patent law. First there was Astbury’s new white body, made with a fixed mixture of powdered flint and Devon clay, imported on horseback from the sea-port of Chester. Twenty years earlier the idea of bringing clay from Devon would have been regarded as madness, and, even in 1720, carts could not get to Burslem, and the clay must have been brought inland on pack saddles. But the invention of the calcined flint body meant also the invention of that terrible disease known as “potter’s asthma” or “potter’s rot,” which used to cause an even greater mortality than lead poisoning. When white flints were first used they were ground and powdered in the dry state, in an atmosphere of flint dust, in underground cellars, so that the secret of this valuable new preparation should not leak out.[44] This state of things was soon partially remedied, for between 1726 and 1732 several patents were taken out—by Gallimore, Bourne, and finally by Benson—for grinding the flint stones in water.[45] Benson’s final process has survived to this day as the universal form of flint mill. A vertical shaft with four radiating arms revolves in a circular horizontal pan. The pan, with a hard stone bottom of chert, is filled with water, and similar chert blocks, pushed round by the arms, grind the flints down to a cream. Flint grinding became an industry, and in the well-watered valleys of North Staffordshire, wherever there was both water-power and flint, these flint mills sprung up and flourished. Though most of them are now closed down through the progress of railways and steam, there are some still to be seen working in the Moddershall valley, whence the creamy slip is sent in by water-cart to Longton.