# Spectroscopic and Microscopic Characterization of Flashed Glasses from Stained Glass Windows
## 3 Results and Discussion
### Chemical Characterization
Pink1 is the only sample in which the chromophores were not detected by FESEM-EDS; however, in the UV-Vis-IR spectrum (Figure 4a), the band of Mn\({}^{3+}\) was detected with a slight shift to higher wavelengths as a result of the high concentration of lead in the colored layer [19]. A low concentration of manganese may color the surface layer with a pink hue, although its concentration could not be high enough to be detected by FESEM-EDS. In the colored layer of the Pink2 piece, CuO was detected by FESEM-EDS. However, no clear band of copper was observed in the UV-Vis-IR spectrum, except for a shift of the absorption front to \(\sim\)560 nm (Figure 4a), a behavior that is related to the plasmon resonance of copper nanoparticles [19]. The chemical composition of the Brown2 sample is similar to that of Pink2 (Table 2), but the color was more intense due to the presence of larger copper nanoparticles and/or a thicker colored layer. In the Brown1 sample, which displays a yellowish hue, high contents of Cr\({}_{2}\)O\({}_{3}\) and Fe\({}_{2}\)O\({}_{3}\) (Table 2) were detected. Some of the bands of Cr\({}^{3+}\) at 630, 650, and 675 nm appeared  
Figure 4: Transmittance spectra of the different colored flashed glasses: (a) pink, (b) brown, (c) blue, (d) black, and (e) green. in the visible spectrum; whereas, the bands at 435 nm (Cr\({}^{3+}\)) and 365 nm (Cr\({}^{6+}\)) are overlapped with the shift of the absorption front to \(\sim\)430 nm (Figure 4b). This shift, shorter than in the Brown2 spectrum, can be attributed to an iron-amber glass [45]. In this case, the chromophore is formed by mixed tetrahedral coordination, in which one Fe\({}^{3+}\) ion is surrounded by three oxygen ions (bonded to silicon) and one sulfide anion (bonded to alkali ions for preserving electro-neutrality) (FeO\({}_{3}\)S). To obtain this color, reductive conditions are necessary during glass fabrication. For this reason, the band at 1100 nm is assigned to Fe\({}^{2+}\) (Figure 4b). The color observed in the surface layer is produced by the overlap of the bands of the different chromophores. Regarding the blue samples, Blue1 has a relatively high content of CuO (\(\sim\)2 wt.%), which is also observed in the visible spectrum by virtue of the broad band of Cu\({}^{2+}\) (Figure 4c). On the contrary, in Blue2 and Blue3, cobalt instead of copper was detected in the EDS analyses. The bands of Co\({}^{2+}\) are clearly observed in the visible spectrum, being saturated in the darker glass (Figure 4c). Blue3 also contains \(\sim\)1 wt.% of ZnO. The presence of this oxide decreases the dilatation coefficient of glasses, favoring their resistance to thermal shock that can be generated in bluish glasses in direct contact with the colorless ones due to their highest NIR absorption [46]. In the Black glass, a high concentration of MnO, CoO, and NiO was detected in the FESEM-EDS analyses. Mn\({}^{3+}\) and Co\({}^{2+}\) ions in high concentration give intense purple and blue colorations, respectively, due to their high molar extinction coefficient. NiO was also detected by FESEM-EDS and by virtue of the bands of Ni\({}^{2+}\) in the visible spectrum (Figure 4d). The color associated with this ion depends on its type of coordination and on the nature of the glass. In silicate glasses, Ni\({}^{2+}\) in tetrahedral coordination produces a violet color, while in octahedral coordination gives a yellow hue. If both types of coordination are present, it is common to find grey glasses. The intense coloration of the three chromophores yields the black color to the colored layer. Finally, in the green glasses, common greenish chromophores such as Cr\({}_{2}\)O\({}_{3}\), Fe\({}_{2}\)O\({}_{3}\), or CuO were detected. Green1 has a high content of PbO (\(\sim\)36 wt.%) together with 4.4 wt.% of TiO\({}_{2}\) and 1.5 wt.% Cr\({}_{2}\)O\({}_{3}\). PbO favors the decrease in the melting temperature of the colored layer, but it also gives a yellowish hue due to the shift of the absorption front into the visible range.