Glass Beads, Markers of Ancient Trade in Sub-Saharan Africa: Methodology, State of the Art and Perspectives

Abstract

Glass beads have been produced and traded for millennia all over the world for use as everyday items of adornment, ceremonial costumes or objects of barter. The preservation of glass beads is good and large hoards have been found in archaeological sites across the world. The variety of shape, size and colour as well as the composition and production technologies of glass beads led to the motivation to use them as markers of exchange pathways covering the Indian Ocean, Africa, Asia, Middle East, the Mediterranean world, Europe and America and also as chronological milestones. This review addresses the history of glass production, the methodology of identification (morphology, colour, elemental composition, glass nanostructure, colouring and opacifying agents and secondary phases) by means of laboratory based instruments (LA-ICP-MS, SEM-EDS, XRF, NAA, Raman microspectroscopy) as well as the mobile instruments (pXRF, Raman) used to study glass beads excavated from sub-Saharan African sites. Attention is paid to the problems neglected such as the heterogeneity of glass (recycled and locally reprocessed glass). The review addresses the potential information that could be extracted using advanced portable methods of analysis.

Non-Invasive On-Site Raman Study of Pigments and Glassy Matrix of 17th–18th Century Painted Enamelled Chinese Metal Wares: Comparison with French Enamelling Technology

“…Hematite is a typical colouring phase of pottery bodies and has been used as a source of red colour since prehistoric times. However, its real use as a red pigment of glass and enamels has only been since the 15th century [2,49], particularly in Limoges [13,26] and Ming cloisonné [12] enamels. Red enamelled areas of cloisonné artefacts display a spectral background characteristic of coloration with metal nanoparticles (see e.g., the F1501 bottle; Figure 6B, and further), as observed for 17th-18th century French enamelled watches [24] and 18th century French porcelain and faience [2].…”

Handheld X-ray Fluorescence (XRF) Versus Wavelength Dispersive XRF: Characterization of Chinese Blue-and-White Porcelain Sherds Using Handheld and Laboratory-Type XRF Instruments

“…Previous studies proved the success of the technique by comparing the data obtained from large-scale instruments, such as time-of-flight ICP-MS with laser ablation (LA), ICP-optical emission spectrometry (ICP-OES), NAA, and energy dispersive XRF. 8,16–21…”

Studying glass on metal: Raman analysis of medieval champlevé enamelled objects

“…The colours blue and turquoise from K 4195 with high As 2 O 3 content are affected by the contribution of As‐O stretching. [ 36 ]…”

“…The colours blue and turquoise from K 4195 with high As 2 O 3 content plot similar to data reported from the high As 2 O 3 glass from glass beads. [ 36 ]…”

“…Maximum wavenumber of Si‐O stretching as function of Si‐O bending; (a) all experimental data from Table S1, ovals indicate glass families from the previous studies [ 12,30,36–38 ] ; soda lime glass with a PbO content above 5% is labelled with “+PbO”; (b) detailed plot of soda lime and mixed alkaline glass, the elements Cu, Sn or Sb indicate the opacifier…”