Soapstone porcelains further added steatite, known as French chalk, for instance at Worcester and Caughley factories. The bone porcelains, especially those of Spode, Minton, Davenport and Coalport, eventually established the standards for soft-paste porcelain which were later (after 1800) maintained widely. Although the Bow porcelain factory, Chelsea porcelain factory, Royal Worcester and Royal Crown Derby factories had, before Spode, established a proportion of about 40–45 per cent calcined bone in the formula as standard, it was Spode who first abandoned the practice of calcining or fritting the bone with some of the other ingredients, and used the simple mixture of bone ash, china stone and kaolin, which since his time set the basic recipe of bone china. The traditional bone china recipe was 6 parts bone-ash, 4 parts china stone and 3.5 parts kaolin, all finely ground together. Josiah Spode I effectively finalised the formula, and appears to have been doing so between 1789 and 1793. It remained an industrial secret for some time. The importance of his innovations has been disputed, being played down by Professor Sir Arthur Church in his "English Porcelain", estimated practically by William Burton, and being very highly esteemed by Spode's contemporary Alexandre Brongniart, director of the Sèvres manufactory, in his "Traité des Arts Céramiques", and by M. L. Solon hailed as a revolutionary improvement. Many fine examples of the elder Spode's productions were destroyed in a fire at Alexandra Palace, London in 1873, where they were included in an exhibition of nearly five thousand specimens of English pottery and porcelain. As the understanding of the work of the early potters depends in part on the study of actual specimens, the loss was both aesthetic and scientific. The business was carried on through his sons at Stoke until April 1833. Spode's London retail shop in Portugal Street went by the name of Spode, Son, and Copeland. Among the many surviving Spode documents are two shape books dated to about 1820 which contain thumbnail sketches of bone china objects with instructions to throwers and turners about size requirements. One copy is in the Joseph Downes collection at Winterthur Museum, Gardens, and Library, Delaware, USA. After some early trials Spode perfected a stoneware that came closer to porcelain than any previously, and introduced his "Stone-China" in 1813.