## 3 Results and Interpretation
### Chemical Composition and Variations
#### 3.3.2 Chemical Variation
In addition, a large concentration of CuO was found in the white impurities (44.16 wt.%). CuO influences the color of the glass during firing, and it may have been added as a coloring material for the brown glass beads from pit tomb No. 12. SEM observations of the light-blue glass beads from tomb No. 18 showed white and gray impurities were distributed in close proximity to each other (Figure 5f). These impurities were largely classified as being round or square in shape, and were quantitatively analyzed separately, as it was expected that the two would have different compositions. The results of the analysis show that although the compositions of the two were generally similar, there were differences in the concentrations of K\({}_{2}\)O, Na\({}_{2}\)O, and SO\({}_{3}\). Although SO\({}_{3}\) was not found in the square impurities, it was found in the round impurities in a low concentration. The concentration of K\({}_{2}\)O in the round impurities was 7.80 to 11.20 wt.%, and the concentration in the square impurities was relatively low with 2.26 to 4.15 wt.%. The concentration of Na\({}_{2}\)O showed the opposite trend: 15.19 to 16.27 wt.% in the round impurities and 21.92 to 22.72 wt.% in the square impurities. The differences in the concentrations of K\({}_{2}\)O and Na\({}_{2}\)O may have resulted from substitution reactions rather than from the effects of fluxes, as K and Na are elements with strong ionization tendencies (Table 3). The surfaces of the brown glass beads from tomb No. 18 were found to contain white impurities, just like the other glass beads (Figure 5g). The impurities were round in shape, and had various sizes ranging from approximately 5 um to 30 um. The results of SEM-EDSanalysis show that the white impurities had large concentrations of CuO regardless of their size; therefore, it is predicted that they were added as coloring materials. However, it is difficult to determine whether CuO was used as a coloring material rather than Fe\({}_{2}\)O\({}_{3}\) in the glass beads from tomb No. 18. Generally, the concentration of coloring material is no more than 5 wt.% of the total composition of the glass, and the analysis of the glass compositions showed that brown glass beads from tombs Nos. 11, 12, and 18 all had less than 5 wt.% of Fe\({}_{2}\)O\({}_{3}\) and CuO (Table 3). In addition, the stereoscopic microscope identified that black materials were present, just like in other types of brown glass, and the brown glass beads from tomb No. 18 used both CuO and Fe\({}_{2}\)O\({}_{3}\) as coloring materials (Table 3). There were white impurities of various sizes and forms in the green glass beads from tomb No. 18 (Figure 5h). The white impurities were less than 20 \(\upmu\)m in size, and the results of the quantitative and qualitative analyses show that there were large concentrations of SnO\({}_{2}\) and PbO: 12.23 to 15.18 wt.%, and 63.44 to 75.79 wt.%, respectively (Table 3). These results are identical to those obtained in the analysis of the green glass beads from tomb No. 11, and it is estimated that PbSnO\({}_{3}\) was added to make the glass beads glossier and opaque.