 Complete the following phrase:  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 Chadwicks 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, 