Sixteenth century tubular glass beads: non‐destructive chemical characterization using synchrotron radiation XRF

The results of a photon microprobe (synchrotron radiation XRF) study of tubular blue glass beads of the Nueva Cadiz type uncovered by recent excavations in the center of Lisbon are reported as a contribution to the non‐destructive chemical characterization of these cultural artifacts, aiming ultimately at ascertaining their provenance and manufacturing location. Either twisted or plain, with round or square cross‐sections, the beads are clearly formed by two blue vitreous layers separated by an opaque white stratum, but a fourth inner transparent bluish layer is visible in the cross‐section of most beads studied. These strata differ essentially in the content of colorant ions (Cu, and occasionally Co traces), fuser metals (essentially Pb) and white layer opacifier (Sn oxide). Other minor and trace elements were determined: K, Ca, Ti, Mn, Fe, Ni, Zn, Ga, As, Br, Rb, Sr, Y, Zr, Nb, Ba, Sb, Hg and Bi. The bromine increase in the outer layers was attributed to burial. Some minor elements are tentatively related to the fuser carrier compound and other chemical components are discussed in terms of raw materials and glass typology.