A rose by any other name: a geochemical comparison of Caughley (c. 1772–99), Coalport (John Rose & Co.;c. 1799–1837), and rival porcelains based on sherds from the factory sites

Compositional data for sherds from various Shropshire factory sites show that at the Coalport works, John Rose and colleagues produced two types of true porcelain that differed in their phosphate content, and bone-ash porcelain. The low-phosphate true porcelain is compositionally similar to its Caughley counterpart; there is, however, no knwn analogue to the relatively phosphatic (0.7–2.7 wt.% P2O5) true porcelain, which appears to have been produced between c. 1795 and the 1830s. All of the analysed Coalport true porcelain sherds are in biscuit, indicating an ‘artificial-porcelain type’ firing sequence. Had they been glazed, the glaze would likely have been lead-rich, as is the case of the glazed true porcelain sherds from the Caughley factory.Soapstone (magnesian) porcelains from the Caughley site resemble Flight-period Worcester porcelain in terms of the concentration of their plastic ingredients (soapstone and clay), but they can have small amounts of fluxing components (lead, alkalis). This indicates that Turner sought to produce a paste with a similar degree of plasticity as Worcester, but he either could achieve and control higher kiln temperatures, or at times was satisfied with a somewhat less vitrified ware. The latter inference is supported by mineralogical and modal melt data, and the rather crude character of some of Turner’s mass-produced wares.Analysed Coalport phosphatic porcelain produced during the decade (1820s) when Nantgarw’s former proprietor (William Billingsley) worked at Coalport has a similar bone-ash/clay ratio (∼ 1.3) but a significantly lower K2O/Na2O ratio (∼ 1.9 versus 5.2) than Nantgarw porcelain. Another Billingsley-related ware, Swansea ‘duck egg’ porcelain (c. 1815–17) has an even more divergent composition, with lower phosphate contents and up to half again as much alumina as Nantgarw and c. 1820s Coalport. The data support the traditional view that Billingsley had little influence on Rose during his tenure at Coalport.