of significant amount of air pollution resulting from the process environmental clean air restrictions led to the demise of widespread use of salt glazing. It was last used on any large scale for the production of salt-glazed sewer-pipes, and other than limited use by some studio potters the process is obsolete, although there are reports of it still being used for sewer-pipes in India. English salt glaze stoneware Experiments in stoneware production began in England during the second part of the 17th century. The earliest evidence has been dated 1650–1700 at the site of a kiln at Woolwich Ferry, London. The similarity of the ware to German products of a similar era has led it to be attributed to immigrant potters. A significant English manufacturer of salt glaze pottery was John Dwight at the Fulham Pottery, which he founded in 1672. In a related patent application, which was granted in 1671, he also claimed to have "discovered the mystery of transparent earthenware commonly knowne by the name of porcelaine or China and Persian ware." By the 1800s Lambeth in London had become a centre for the production of salt glaze stoneware, and most especially after the establishment of Doulton and Watts Pottery, which later became Royal Doulton. The company was founded in 1815 when John Doulton formed a partnership with the owner, Martha Jones and foreman, John Watts, of an existing pottery in Lambeth. Initially the factory specialised in utilitarian salt glazed stoneware, similar to that produced by the Fulham factories. During the 1830s and 1840s, considerable amounts of salt-glazed sewer-pipes were produced by Doultons following Sir Edwin Chadwick's advocacy of improved sanitary conditions. Doultons were also one of the earliest manufacturers of electrical insulators, initially using salt glaze stoneware and for the electrical telegraph systems. Also, from about 1830, they started production of salt glaze stoneware vessels, which were valued for their acid resistance, for the emerging chemical industries. From the 1850s Doulton & Co.'s decorative stoneware, that was produced in association with the nearby Lambeth School of Art, enjoyed significant success at various international exhibitions, including at The Great Exhibition in 1851, Philadelphia Exhibition in 1876, and also at Chicago in 1893. Their salt glaze decorative products became known as 'Doulton Ware'. By 1890 their decorative stoneware were so successful that 350 designers and artists were employed at the Lambeth factory, including the famous George Tinworth. Doulton’s Lambeth