The production technology of mineral soda alumina glass: A perspective from microstructural analysis of glass beads in Iron Age Taiwan

Abstract

Mineral soda alumina (m-Na-Al) glass is a common glass production group found around the Indo-Pacific region. In Iron Age Taiwan, its presence dates back to the early 1st millennium AD. This research discusses m-Na-Al glass beads excavated from Iron Age sites in Taiwan. No production sites for m-Na-Al have been found, but microstructural analysis suggests m-Na-Al glass appears to originate around South Asia and is exchanged widely. SEM-EDS and EPMA were used to analyse red, orange, yellow, green and blue m-Na-Al glass. The microstructure of the glass shows the presence of plagioclase and alkali feldspar relics in the glass, suggesting a low manufacturing temperature. Copper-based colourants are identified in red, orange, blue and green glass, while lead tin oxide is used in yellow and green glass. It appears that various types of copper-containing raw materials were procured by craftspeople, and a self-reduction process for producing red and orange glass is tentatively proposed. Additionally, the microstructure of yellow glass reveals different colouring paths were used. These results increase our understanding of the selection of raw materials, and provide an impetus for further research on the cross craft interaction between glass and copper production.

Counterfeit Glass Beads during the East African Caravan Trade: Mineralogical and Gemmological Analysis

“…Based on the analysis results in this article, it turns out clear that the beads thought to be standard glass beads are indeed made of pure glass obtained from quartz silicate, a typical raw material used to produce Venetian glass beads in production centres in Italy. However, it is well documented that alumina was another important ingredient in the production of glass beads (Dussubieux et al 2010), as it improves the properties of soda-lime-silicate glasses and inhibits devitrification (Wang, Iizuka, & Jackson 2022). Nevertheless, the value of alumina oxide content recorded in the allegedly counterfeit glass beads under discussion is extremely high, up to 90 percent of the material composition.…”

“…Previous studies have shown that alumina content may indicate the region from which the glass was made since these materials match the geochemistry of the area where the silica sources, whether crushed quartz or sand, originate (Wood et al 2009;Dussubieux et al 2010;Wang, Iizuka, & Jackson 2022). It has been found that granite sand generally produces glass in which the proportion of alumina is much higher than that of lime, while lime sand from coastal deposits results in glass with a higher proportion of lime than alumina (Wood et al 2009).…”

Recent Developments in the Archaeology of Long-Distance Connections Across the Ancient Indian Ocean

“…They include the key Funan sites Angkor Borei (Cambodia) and Oc Eo (Vietnam), which also have agate and carnelian beads that suggest links with western India and garnet beads that are compositionally similar to south Indian garnet (Carter et al 2021). South Indian/Sri Lankan Indo-Pacific glass beads are also increasingly recognized at East Asian sites (primarily in elite mortuary contexts) in Taiwan (Wang et al 2022), China (Xu et al 2022a, and Japan (Katsuhiko & Gupta 2000). Korea also has glass beads from this period (Lankton & Dussubieux 2006) as well as carnelian and agate beads drilled with a special technique originally developed in South Asia (Glover & Kenoyer 2019).…”