*3.3. Glassy Matrix*

Raman spectra of the glazes/painted overglaze enamels showed the characteristic signature of glassy silicates, which basically include Si–O bending and stretching bands in the range ~500 and ~1000 cm−<sup>1</sup> , respectively. A comparison of the Si–O stretching band components and the area ratio of the Si–O bending/stretching band has proved to be very efficient for the compositional classification of different glass/glaze/enamel types based on experimental Raman data obtained for a great deal of ancient glassy objects [68–71] as well as on Density Functional Theory calculations [72]. The glazes were aluminosilicate glazes, with the Si–O stretching bands varying between ca. 900 and 1200 cm−<sup>1</sup> . The painted enamels analyzed displayed a broad and strong band varying between ~920 and 1070 cm−<sup>1</sup> with various shoulders/components, indicating mainly lead-based compositions [69–71], as observed for soft-paste porcelains [17] and enameled metalware [14,18]. In some of the spectra, the intensity of the Si–O bending modes near 500 cm−<sup>1</sup> appeared to be equal to or weaker than that of the stretching modes at 950–1050 cm−<sup>1</sup> (see e.g., Figure 6A(c),C(a), Figure 10B(b) and Figure 13B(a',a")). This indicates a polymerization ratio close to less than 1, according to firing at temperatures inferior to 900–1000 ◦C [68,71]. The painted enamels can be further classified into three main glass types (Table 3) based on representative glass (and glaze) types [12,13,16,68,69] and previous studies conducted on Chinese *cloisonné* and painted enamels [10,14,73–76]: (i) lead-rich glass with the strongest component at ca. 920 to 1020 cm−<sup>1</sup> (Type I); (ii) lead (earth) alkali glass with the strongest component at ca. 1030 to 1060 cm−<sup>1</sup> (Type IIa), with rather similar-intensity components at ca. 980 and 1040 cm−<sup>1</sup> (Type IIb); and (iii) lead (earth) alkali glass with the strongest component at ca. 1070 cm−<sup>1</sup> (Type III). Some of the yellow, green and black enamels belonged to the lead-rich type of glass, with their strongest component

at low wavenumbers, which indicates a low degree of polymerization and firing at low temperatures (the addition of Naples yellow increases the lead content). Most of the painted enamels (white and blue) belonged to the lead alkali type of glass (the addition of smalt increases the potassium content), with their strongest component shifted to higher wavenumbers (up to ca. 1060 cm−<sup>1</sup> ) accompanied by a similar low wavenumber component to the lead-rich glass. The glass compositions of the painted enamels did not show much variety, indicating a limited number of firings over the transparent glaze.

**Table 3.** SiO<sup>4</sup> stretching components of the glassy matrix of the painted enamels analyzed (strongest; *shoulder*/*weak*) and comparison with Chinese enameled metalware (Lead alkali glass: L-a; Lead-rich glass: L-rich).

