Abstract:
Tracing the origin of glass trade beads excavated at archaeological sites
can contribute significantly to dating a site and reconstructing prehistoric trade
routes. Wood developed a temporally sensitive bead sequence dating from the 8th
to the 16th century AD for beads excavated at southern African sites that is
commonly used by archaeologists to classify beads according to their
morphology. In this study we develop a multidisciplinary methodology to refine
the classification of glass beads based on morphology alone. Glass trade beads
excavated at 11 sites along the upper reaches of the Limpopo River in east-central
Botswana are used as case study. The beads were visually classified according to
their morphological properties (colour, size, etc.) and analysed with Raman
spectroscopy and portable X-ray fluorescence (XRF). Energy Dispersive
Spectroscopy (EDS) of one bead showed that two types of glass were sintered
together to form a recycled product, explaining the divergence of Raman spectra
recorded on different zones. The study confirms the value of a morphological
classification based on existing data sets as a first approach, but demonstrates that
both Raman and XRF measurements can contribute to a more exact classification
of glass beads imported into southern Africa from the East before the 17th century
AD.
