3 Analytical report of glass beads from Hoa Diem site, Khanh Hoa, Viet Nam.

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1 3 Analytical report of glass beads from Hoa Diem site, Khanh Hoa, Viet Nam. Yoshiyuki Iizuka (Institute of Earth Sciences, Academia Sinica) Studied glass beads are listed and shown in Table 1 and Figure 1, respectively. Table 1 Studied glass beads from Hoa Diem site, Khanh Hoa, Viet Nam. No. Color Material Inclusions Structure of interior Holder-1 N1 10HD-H3 M3 dark blue K-Mn glass homogeneous N2 10HD-H1 M7 green Na-Pb glass Sn, Pb, (solder) heterogeneity N3 07HD-H1 M2 green Na-Pb glass Sn, Pb, (solder), zircon layered N4 07HD-H1 M8 green *Cu-Oxide granular N6 07HD-H1 B3.C3 blue K glass layered Holder-2 N5 07HD-H1 M3 green Pb glass homogeneous N7 07HD-H1 B3.C3 brown-white # Quartz massive N8 07HD-H1 M8-1 blue Na-glass homogeneous Note: K: potash glass; Na: soda glass; Pb: lead glass; *: Copper bead; # : agate bead. Fig. 1 Studied glass beads before sample preparation. Scale:1 mm. 9

2 Analytical procedure To observe internal section of glass beads and to identify their chemistry, the samples were sliced in a small piece (less than few mm in size with few mm in thickness) by a micro-diamond saw. To avoid damage the original texture of the glass during the cutting process, rotation speed of the diamond saw was operated in 100 r.p.m. with the distilled water for cooling. Cleaned samples by ethanol were mounted in a cold-mounting (room temperature cured for an over night) epoxy resin with 1-inch diameter mold and exposed surfaces were well polished with Alumina paste (Fig. 2). Fig. 2 Polished section of glass beads and their working number. Polished sections were initially observed by an optical microscope with the reflection lights. Then, a scanning electron microscope (SEM: JEOL JSM-6360LV) was used to observe micro-scale texture. Semiquantitative analysis of the glass were carried out by an energy dispersive spectrometer (EDS: Oxford Instruments Ltd., INCA-300) which equipped on the SEM, under the primary beam conditions of 15 kilo Volt (kv), and 30 pico Ampere (pa) for the acceleration voltage and the beam current, respectively, in the vacuum condition of 25 Pa (Pascal), that the beam power and X-ray counting time (beam exposure time) is enough low and short (30sec), respectively, to avoid beam damage on the surface of glass. Analyzed points or areas were selected with the back-scattered electron images to avoid some damaged or vacant spaces. Results Results of SEM-EDS observation and chemical compositions are shown in Tables 1 and 2, respectively. Samples No. 4 (07HD-H1.M8) and No. 7 (07HD-H1 B3.C3) are Cupper oxide (probably CuO) and silica (SiO 2 ), likely quartz, respectively. Both are not glass beads, namely copper and agate beads. Others are silica glasses with alkaline elements (Na and K), and/or lead, but alumina (Al 2 O 3 ) contents are rather lower (approx. 10

3 Part IV 3 Analytical report of glass beads from Hoa Diem site, Khanh Hoa, Viet Nam. 2 to 4 wt.%). Back-scattered electron micrographs of section of glass beads are shown in Fig.3. The images represent mean atomic abundance by contrast in black and white from the polished surfaces. Thus, if there is chemical heterogeneity in the glass, heavier and lighter elemental compounds are represented by higher- and darker contrast. Some of defect of glass, such as holes and cracks are shown in darker contrast. Observation results from the back-scattered micrographs and EDS are described as follows; No. 1 (10HD-H3.M3): Potash glass. Few amount of MnO contains in the glass. A numbers of holes, which should be remains of air bubbles of few 10s to 200μm in diameter, are observed as dark or bright circles. Layered dispose of the holes are observed. It is likely a pulling structure during glass making. Rim is slightly altered and it is shown as darker contrast. No. 2 (10HD-H1.M7): Soda lead glass with solder (tin-lead alloy), lead and tin particles. Chemical heterogeneity is significant. Air bubbles, few 10s to 300μm in diameter, are observed. Solder (tin-lead alloy), lead and tin are observed as highest contrast regions and spots. Rim is slightly altered and it is shown as darker contrast. No. 3 (07HD-H1.M2): Soda lead glass with solder (tin-lead alloy), lead and tin particles. Air bubbles (10-50μm in diameter) are observed as dark circles. Solder (tin-lead alloy), lead and tin are observed as highest contrast stripes and 11

4 spots and their layered structure is clearly observed. It is likely a pulling structure during bead making process. Rim is seriously altered and it is shown as darker contrast. No. 4 (07HD-H1.M8): Copper bead (copper oxide; not glass). Structured dispose and cracks are observed. Rim is seriously oxidized and it is shown as darker contrast. No. 5 (07HD-H1.M3): Lead glass. Chemical heterogeneity is slightly observed in micro-scale by the contrast. No. 6 (07HD-H1.B3.C3): Soda-potash glass. Layered chemical heterogeneity is slightly observed. It is likely a pulling structure during glass making. Air bubbles, 10 to 50μm in diameter, are observed. No. 7 (07HD-H1 B3.C3). Quartz. It can be named as agate bead. No. 8 (07HD-H1.M8-1): Soda-potash glass. Chemical heterogeneity is not observed. Air bubbles, 10 to 100μm in diameter, are observed. Along the cracks and rim are seriously altered as shown in darker contrast. Conclusive remarks SEM-EDS techniques have been applied for glass beads analysis. It is definitely destructive analysis; however, we could obtain several kinds of information from the interior of glass beads. In the many of cases, surfaces of glass beads are not well preserved in terms of chemistry that serious oxidation has been occurred probably during burial. In general, silica and alkaline elements, such as Na and K, are strongly affected by hydration and its chemical composition is altered eventually. It suggests that both non-invasive surface analysis and whole glass chemistry by solution method are not able to obtain the original chemistry of glass beads because it might contain altered portion. Observation of micro and chemical structure of bead s interior might indicate its making technique. In this study, many of micro-grains of Lead, Tin and solder (Sn-Pb alloy) were observed from the interior of lead-glass beads. It is likely that these are the flux for fusion process. Moreover, structure observation indicates that some of glasses show chemical heterogeneity. This result suggests that such glass, shown layered structure, is not melted well or not mixed well during glass making process. Thus observation of bead s interior under SEM-EDS is a way to understand its chemistry and bead making process. From conservational point of view, destructive analysis is not acceptable for study of cultural properties. However, if an abundance of glass beads are collected, it is worth applying the SEM-EDS analysis and more advanced techniques for study glass beads, which is shown in this report. 12

5 Table 2 Chemical composition of glass beads. in wt.% SiO 2 Al 2 O 3 MnO CaO Na 2 O K 2 O SnO 2 PbO CuO Total No. 1 (Mean) No. 2 (Low-Pb portion) No. 2 (High-Pb portion) No. 3 (Low-Pb portion) No. 3 (High-Pb portion) No. 4 (Mean) No. 5 (Mean) No. 6 (Mean) No. 7 (Mean) No. 8 (Mean) Mean value: averaged by 3-5 area analysis. Analytical results are normalized in 100%. 13