Without Astbury,[30] who is said to have died in 1743, aged 65,[31] it is doubtful whether even salt glazing could have been a really great success. He it was that obtained a body white enough to show off the transparent salt glaze to the best advantage. Dr Thomas Wedgwood had only the drab body to work on—a far less effective medium. With the object of whitening the clay body, Astbury began to import the white clays of Devonshire.[32] At first he used them only as a wash or dip to whiten the surface of the ware, just as the tin-enamel had been used to conceal and coat the coarse body of the Delft ware. Then he developed the use of the white sands of Baddeley Edge and Mow Cop to harden the body; and, in 1720, according to tradition, he made the really vital discovery of the value of calcined flint stones for both these purposes—to whiten and to harden the clay body from which the stone ware was made. Josiah Wedgwood, writing in 1777, attributed this discovery to a potter of Shelton called Heath instead of to Astbury,[33] but whoever it was that first noticed the whiteness of burnt flints, it was Astbury who first determined the value of the new material and the manner of using it. This discovery marks the first stage in the production of cream-coloured earthenware as well as in the production of the perfect salt glaze.[34] Astbury and his son Thomas made red and black ware also, after the pattern of Elers, but with this difference, the ornamentation of Astbury’s red or black ware is generally done in white clay,[35] instead of in the same colour as the body; and this is one sign by which collectors distinguish these two makers. Robert (or John) Astbury was succeeded by his son Thomas, who had started potting at Lane Delf in 1725. Their name does not occur among the potters of the latter half of the eighteenth century, but Margaret, Thomas Astbury’s daughter, married Robert Garner, a master potter of Longton, who attained a considerable position. Joshua Twyford (1640-1729), like Astbury, had his factory in Shelton; one stood on either side of the mound where the church now is. Twyford is best known for his stoneware, chiefly red and black in the style of Elers, but he is also supposed to have made salt-glazed ware.