Geochemistry of sauceboats excavated from Independence National Historical Park (Philadelphia): evidence for a Bonnin and Morris (c. 1770e73) provenance and implications for the development of nascent American porcelain wares

摘要

Porcelain sauceboats excavated from a privy with a late 18th century (1786 or later) context at Independence National Historical Park (INHP) are anomalously Al-rich compared with previously analysed Anglo-American sulphurous phosphatic wares. Apart from their S content, they are most similar to phosphatic W~m Reid porcelain (Brownlow Hill, Liverpool, c. 1755-67, and its branch at Shelton, Staffordshire) in terms of their major element constituents, but they contain heavy minerals (e.g., TiO_2 polymorphs) and in this regard resemble a dated (1773) silicious-aluminous-calcic (S-A-C) Bonnin and Morris porcelain (Philadelphia) openwork porcelain basket. In terms of morphology and composition, some TiO_2 polymorphs in the 1773 basket match those from clay from White Clay Creek, Delaware, a resource reputedly exploited by Bonnin and Morris. Their high Nb/Cr ratios indicate derivation from a metapelitic (or granitic pegmatite) source. So too do some from the INHP sauceboats, although others are chrome-rich (～1% Cr_2O_3), indicating a mafic source. The bedrock beneath White Clay Creek includes metasediments, granitic pegmatite, and metabasites (e.g., of the Wissahickon Formation), pointing to a local source for the TiO_2 polymorphs in the porcelains described here. Although the evidence for a Bonnin and Morris provenance for the INHP sauceboats is circumstantial, their enrichment in heavy minerals, unusual - perhaps experimental - compositions, and aesthetic characteristics nonetheless suggest a Philadelphia origin for these artifacts. The compositions of 18th century Philadelphia porcelain support the contention that knowledge of phosphatic and S-A-C pastes originating in London was transferred first to Staffordshire and Liverpool, and then to Philadelphia, perhaps via a potter by the name of Wm Ball.