Optimal Elemental Characterization of Historical High-Fired Ceramic Wares: Majors/Minors, Traces, or Both?

Porcelain wares containing calcined bone ash and gypsum in their pastes were some of the most commercially successful high-fired wares produced in Britain and America during the third quarter of the 18th century. They were produced by the two earliest porcelain manufactories in America (the Bartlam and the Bonnin & Morris factories) and by several British manufactories, including the largest such enterprise (Bow) and another London factory (Isleworth). Owing to the influence that London manufacturers had on contemporary and later porcelain producers elsewhere in Britain and in America, major, minor, and high-precision trace-element data were determined for pastes and glazes of potsherds from the sites of these factories so that compositional commonalities and differences could be ascertained. Multidimensional scaling of major- and minor-element data for 34 samples of these wares generates diagrams on which the products of the four factories under consideration cluster relatively tightly as compared with diagrams created using only trace elements and all analytical data (major, minor, and trace elements). The coupling of geochemically unaffiliated components (or ratios thereof), including trace elements, however, tends to generate the best field separation on discrimination diagrams for these wares. The American and British phosphatic porcelains described here can readily be distinguished based on the concentrations of various paste components; rubidium vs. arsenic and tin, for example, best distinguishes Bartlam from Bonnin & Morris and their London counterparts.