# Spectroscopic and Microscopic Characterization of Flashed Glasses from Stained Glass Windows
## 3 Results and Discussion  
### Thickness Measurements  
The different colored layers on the base glasses from the considered flashed glass samples were measured by OM and FESEM-EDS. Analysis of the flashed glasses by OM (Figure 2 and Table 1) showed a structure of parallel layers with a large range of thicknesses for the colored layers. Following the Lambert-Beer law, the thicker the colored layer, the higher the intensity of the color. Nevertheless, some of the pieces with thin layers showed dark colorations due to a high concentration of chromophores. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & \multicolumn{3}{c}{**Thickness (\(\upmu\)m)**} \\ \cline{2-4}
**Sample** & **OM** & **FESEM** & **Linear FESEM-EDS Analyses** \\ \hline Pink1 & \(137\pm 1\) & \(147\pm 1\) & - \\ \hline Pink2 & \(127\pm 1\) & - & 106–206 \\ \hline Brown1 & \(331\pm 2\) & \(334\pm 2\) & - \\ \hline Brown2 & \(351\pm 1\) & - & 306–403 \\ \hline Blue1 & \(675\pm 1\) & & 652–747 \\ \hline Blue2 & \(173\pm 2\) & - & 176–226 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Thickness of the colored layers measured in the cross-section of the glasses using OM, FESEM, and chemical linear analyses with FESEM-EDS. Figure 2: OM images of the colored layers on the flashed glasses in cross-section. Colored layer (**top**) and base glass (**bottom**). All the samples have the same scale. The pinkish and brownish glasses showed similar thicknesses; however, the bluish and greenish ones displayed completely different thicknesses. It is also interesting to note that the Blue1 and Green2 samples present a multilayer structure that could be related to their fabrication processes. The Brown2 and Blue3 glasses showed a non-homogeneous coloration in cross-section that can be related to the diffusion of the colored layer into the base colorless glass or that the fragment was not completely perpendicular in cross-section, inducing an optical effect of color fading. The same set of glass pieces was inspected by FESEM-EDS and two different behaviors were detected. Some of the pieces (Pink1, Brown1, Black, Green1, and Green3) showed a clear surface layer that corresponds to the colored one, but the other samples behave differently (Figure 3). The differences in the hue shown in the micrographs are related to the dissimilar chemical composition (Section 3.2.) and not to the contribution of chromophores in the layer, as these could not be detected by FESEM-EDS due to their low concentrations. In the samples with a clear layer, FESEM-EDS thickness measurements were comparable to those quantified by OM (Table 1); however, when this layer was not observable, the thickness was estimated through FESEM-EDS linear analyses by determining the profile of the chemical concentration of different elements (Figure 3). In the Pink2, Brown2, Blue2, and Blue3 samples, it was observed that the surface layer has a higher concentration of potassium or cobalt than the base glass; however, the thickness of the surface layer on the Green2 sample was estimated using calcium element, which pres \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multicolumn{3}{c}{**Thickness (\(\mu\)m)**} \\ \cline{2-4}  & **OM** & **FESEM** & **Linear FESEM-EDS Analyses** \\ \hline Blue3 & \(386\pm 2\) & - & \(373\)–\(391\) \\ \hline Black & \(175\pm 1\) & \(177\pm 2\) & - \\ \hline Green1 & \(193\pm 2\) & \(195\pm 1\) & - \\ \hline Green2 & \(352\pm 1\) & - & \(235\)–\(314\) \\ \hline Green3 & \(175\pm 1\) & \(180\pm 2\) & - \\ \hline \hline \end{tabular}
\end{table} 
Table 1: _Cont._  
Figure 3: FESEM images of the colored layers in the flashed glasses in cross-section. The scale is the same for all the images. in the colored layer in comparison with the base glass (Figure 3). The thickness was estimated as a range between the following two values: the depth at which the composition of the colored layer loses its homogeneity and the depth when the homogeneous material of the base glass appears.