The Staffordshire Potteries is the industrial area encompassing the six towns Burslem, Fenton, Hanley, Longton, Stoke and Tunstall, which is now the city of Stoke-on-Trent in Staffordshire, England. North Staffordshire became a centre of ceramic production in the early 17th century, due to the local availability of clay, salt, lead and coal. Hundreds of companies produced all kinds of pottery, from tablewares and decorative pieces to industrial items. The main pottery types of earthenware, stoneware and porcelain were all made in large quantities, and the Staffordshire industry was a major innovator in developing new varieties of ceramic bodies such as bone china and jasperware, as well as pioneering transfer printing and other glazing and decorating techniques. In general Staffordshire was strongest in the middle and low price ranges, though the finest and most expensive types of wares were also made. By the late 18th century North Staffordshire was the largest producer of ceramics in Britain, despite significant centres elsewhere. Large export markets took Staffordshire pottery around the world, especially in the 19th century. Production began to decline in the late 19th century, as other countries developed their industries. After World War II it declined steeply. Production continues in the area, but at a fraction of the levels at the peak of the industry. The boom came after the discovery in 1720 by potter John Astbury of Shelton, that by adding heated and ground flint powder to the local reddish clay he could create a more palatable white or Creamware. The flint was sourced from either the South Coast of England or France, then shipped to the Port of Liverpool or to Shardlow on the River Trent. After shipping by pack horses to the watermills local to the potteries, or to commercial flint grinding mills in either the Churnet Valley or Moddershall Valley, it was sorted to remove flint that had reddish hues, then heated to to create an easily ground product.