XRF analysis of White Glass Beads from Mission San José: Assessing Rapid Characterization for Chronological Placement

The elemental analysis of glass beads has great potential for the archaeology of California’s colonial and Indigenous pasts. The present study employs a sample of 535 white glass beads from Mission San José (1797-1840s) to evaluate the usefulness of x-ray fluorescence (XRF) analysis for identifying temporally-diagnostic glass opacifiers, particularly antimony and arsenic, which are not visible to the naked eye. Our results indicate that the majority of the beads in our analysis were opacified with antimony, with several that exhibit evidence of arsenic as an opacifying agent. Consistent with previous research from Spanish colonial sites in central California, our study supports a mid-nineteenth century (1840s-1850s) introduction of arsenic-rich beads to the region. Overall, this study illustrates the strengths of utilizing rapid XRF analysis to differentiate glass bead opacifiers, while further confirming the regional introduction of arsenic opacifiers during a critical period in the history of Native California.