Beyond sourcing: portable X-ray fluorescence and archaeological ceramics

Handheld portable X-ray fluorescence (pXRF) technology has been increasingly employed in ceramic provenance studies. While these applications have been largely successful, the utility of this technology for ceramic analysis has nonetheless been called into question. This thesis considers the utility of pXRF for the analysis of archaeological ceramics. It is argued that the analysis of ceramics using any geochemical technique must recognize and account for the range of environmental and technological factors that influence ceramic composition. Ceramics are synthetic and heterogeneous, and thus present a special set of challenges for analysis using non-destructive techniques such as pXRF. Variability in pXRF analysis is assessed in this thesis at both the level of the individual artifact, and at the level of the assemblage. Archaeological ceramics from sites in Fiji, Tonga, and Jamaica are analyzed using pXRF to assess analytical variability from the perspective of “repeatability”. Substantial variability is evident in the results of repeat, sequential measurements of individual ceramic sherds. In particular, consistent differences are observed between the “core” and “surface” of the sherds. Variability generally increases when larger temper grains are present in the paste matrix. Analytical variability, therefore, appears to relate to both the compositional properties of ceramics, as well the known parameters of non-destructive pXRF analysis. A case study using pXRF to characterize an expanded sample of Fijian ceramics demonstrates the efficacy of a geochemical inventory strategy for identifying compositional differences within and between assemblages. This thesis highlights the need for independent theory and protocol governing non-destructive analysis of ceramics. The unique capabilities of pXRF are best exploited when the physical properties of specimens and the analytical parameters of the technique are critically examined in tandem. That pXRF analysis “averages” the geochemistry of the ceramic paste constituents is, in light of this broader understanding of ceramic composition, actually advantageous.