Determining the provenance of the European glass beads of Lumbu (Mbanza Kongo, Angola)

Abstract

A collection of glass beads found in Lumbu (Mbanza Kongo, Angola) were analyzed by means of a multi-analytical minimally invasive methodology, which included handheld X-ray fluorescence (hXRF), variable pressure scanning electron microscope coupled with energy dispersive X-ray spectrometry (VP-SEM-EDS), micro-Raman spectroscopy and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Trace element analysis, and rare earth element pattern analysis in particular, was found to be essential to establish the provenance of the European trade beads in this study. The glass beads from types 30, 31, 32, 36, 38, 39, 40, 41, 42, 43 and 45 were found to have been produced in Venice, and the glass beads from types 26 and 28 have been assigned to the Bohemian glass industry. While determining the provenance of each glass artefact was a major goal of this study, the process of glass coloring and opacification was also studied in an attempt to establish the technology employed in the production of these artefacts. Chemical data indicate that cobalt and copper were used to produce blue hues, while a combination of copper and iron ions was used to produce green glass. Black colored glass was obtained by the combined use of iron and manganese ions, whereas the iron-sulfur chromophore was used to impart a distinct amber hue to the glass. Red was produced using trace amounts of metallic gold particles (ruby red glass) and metallic copper nano-particles or cuprous oxide (brownish-red glass). Lead arsenates, calcium phosphate, and cassiterite were used as opacifying agents. The use of both morphological and chemical analysis enabled the identification of distinct European production centers, allowing a glimpse into the consumption patterns and economic interactions in place between Europe and West-Central Africa throughout the 17th-19th centuries.