Fig 1.
Map showing the location of study sites (above), and bead samples from each site (below).
(Map made with Natural Earth. Free vector and raster map data @ naturalearthdata.com.).
Table 1.
Summary of the study sites and the context of excavated glass beads.
Fig 2.
BSE image showing the heterogeneous microstructure of the glass matrix.
Fig 3.
A plot of m-Na-Al glasses in the Na2O-Al2O3-SiO2 phase diagram.
The oxides from the base composition are further reduced into three components (SiO2, Al2O3* and Na2O*)–the FeO, MgO and CaO are transmuted to Al2O3 (labelled Al2O3*), using a transmuting factor of 0.71, 1.26 and 0.91, respectively (Rehren 2016, pers. comm.). The K2O is incorporated into Na2O (labelled Na2O*) transmuted by the factor of 0.66. The base phase diagram is from Levin and McMurdie [23].
Fig 4.
BSE image showing the relics in red glass, in which (a) silver particles are observed in copper sulphide inclusion (JXL02), (b) a copper oxide inclusion showing partial reduction process (JXL10), (c) a metallic copper inclusion showing partial oxidation (GS004), and (d) a cluster of needle-like tin oxide remain the crude cassiterite shape (JXL22).
Fig 5.
BSE image showing the microstructure of orange glass, in which (a) copper-bearing crystals of micro size distribute linearly over the glass matrix or fill within round voids (JXL27), (b) large copper oxide crystals are found in the red striae, while the particles of sub-micron size spread over the orange matrix (JXL24), (c)-(e) oxidised bronze prill was observed (JXL25, wt%), (f) a cluster of copper oxide and tin oxide suggesting decomposition from bronze (KWL005), and (g) large metallic copper crystals are confirmed by EDS (KWL003).
Table 2.
Chemical composition in relation to the use of copper colorant.
Fig 6.
BSE image the microstructure of blue glass, in which (a) clusters of copper oxide (grey) and tin oxide (bright) (JXL28) and (b) the prismatic barite inclusions (JXL17) are observed.
Fig 7.
BSE image showing microstructure of yellow glass, in which (a) clusters of tiny lead tin oxide crystals are frequently found with large and newly formed nephelines in Case 1 (JXL15), (b) the cores of Pb(Sn,Si)O3 exhibits possible Pb2SnO4 remnants (JXL05), (c) lead tin oxide clusters solely, without any nepheline, in Case 2 (DY14), (d) porous bone ash is observed (GS028), and (e)-(f) Ba-bearing K-feldspar and lead tin oxide is found in the bone ash-containing samples, and the bone ash is particularly high in PbO (>60wt%) (JXL48).
Fig 8.
BSE image showing microstructure of green glass, in which (a) a tin oxide rich in Fe, Zn and Ni is found (DY42-1), (b) a tin-rich inclusion containing Ca, Al and Si is observed (GS103), and (c) a visible red inclusion showing inhomogeneous distribution of CuO, TiO2, FeO and SO3, as well as prismatic barite crystals and partially melted sodium aluminosilicate (JXL09).