# Spectroscopic and Microscopic Characterization of Flashed Glasses from Stained Glass Windows
## 2 Materials and Methods  
The study was conducted in a set of 11 flashed glasses, provided by LambertsGlas(r), consisting of a colorless base glass covered by layers of different colors and thicknesses (Figure 1).  
The samples were compositionally and structurally characterized by OM, FESEM-EDS, UV-Vis-IR spectroscopy, LIBS, and LIF.  
OM observations were carried out with a reflected light microscope Nikon SMZ1000 coupled to an Axiocom 105 color controlled with the software Zen2012 (blue edition) from Carl Zeiss Microscopy GmbH, 2011. Cross-section examinations and chemical linear analyses were performed by a field emission scanning electron microscope HITACHI S 4700. For elemental chemical linear analysis by EDS, a NORAN system six was connected to the FESEM.  
Transmission spectra of original glasses were recorded with a Perkin Elmer Lambda 950 UV-Vis-IR spectrophotometer. The illumination was provided by a tungsten-halogen and deuterium light source in a double optical path covering the 200-2500 nm range with a resolution of 10 nm.  
LIBS analyses were performed upon laser excitation at 266 nm (4 th harmonic of a Q-switched Nd:YAG laser, 15 ns pulses, 1 Hz repetition rate) and a 0.2 m spectrograph (Andor, Shamrock Kymera-19 Si-A) equipped with a grating of 1200 grooves/mm, blazed at 500 nm. The output of the spectrograph was coupled to an intensified charge-coupled device (ICCD) camera from Andor Technology, Belfast, Ireland (iStar CCD 334, 1024 \(\times\) 1024 active pixels, 13 \(\upmu\)m \(\times\) 13 \(\upmu\)m pixel size). The laser beam was steered to the surface of the samples at an angle of 45\({}^{\circ}\) by using different mirrors. A cut-off filter of 300 nm was placed at the entrance of the spectrograph to reduce the scattered laser light and avoid second-order diffraction. The shot-to-shot fluctuation of laser pulse energy was less than 10%. The laser beam was focused on the surface of the sample with a 10 cm focal length lens achieving a fluence of 8.3 J cm\({}^{-2}\) (2.6 mJ per pulse in a 200 \(\upmu\)m laser spot diameter). The spectra were recorded at 50 nm intervals in the 230-300 nm wavelength range and step and glue spectrograph mode in the range of 300-600 nm with 0.2 nm resolution and with a gate delay and width of 200 ns and 3 \(\upmu\)s, respectively, with respect to the arrival of the laser pulse to the sample surface. The spectra resulted from summing up the emissions of the ablation products after ten successive laser pulses, a number that provided good signal-to-noise ratios.  
For the LIF measurements, we used the same laser source as for LIBS analysis and a 0.30 m spectrograph (TMc300 Bentham) blazed at 500 nm with a 300 grooves/mm grating coupled to an ICCD, 2151 Andor Technology device, Belfast, Ireland. In this case, the time gate was operated with a zero-time delay with respect to the arrival of the laser pulse to the sample surface and with a width of 3 \(\upmu\)s. The sample was illuminated at an incidence angle of 45\({}^{\circ}\) through a pinhole, to select the central part of the unfocused laser beam, giving rise to a spot on the sample of elliptical shape with axes dimensions between 1 and 2 mm and with fluences of around 6 \(\times\) 10\({}^{-3}\) J/cm\({}^{2}\). LIF spectra were recorded at 300 nm intervals in  
Figure 1: Images of the flashed glasses considered in the present study.  
the wavelength range of 300-700 nm with 5 nm resolution. A cut-off filter at 300 nm was also used for the LIBS measurements. Each spectrum resulted from the accumulation of 10 individual ones.