## 3 Results
### Light Characterization of the WG-Coated Specimens  
Measurements of the whiteness index L* and light spectral reflectance measurements were taken for the 27 specimens described above. Table 3 shows the value of L* for the three WG-coated samples. In this table, WG1Q1 stands for the sample with a coating thickness of Q1 (Table 1) and so on. As can be observed in this table, the whiteness index ranged from 50.45 to 52.93, with an average value of 51.78, for WG1; it ranged from 49.24 to 55.23, with an average value of 52.93, for WG2; and it ranged from 54.54 to 100, with an average value of 84.49, for WG3. An ANOVA analysis according to the methodology section was also performed on the data coming from Table 3, and all the results can be found in Appendix A. The statistical results coming from the nonparametric Mann-Whitney U test showed the following:  
* In general, the variables \"holding time of burning\" and \"thickness of WG coating\" had no significant influence on the whiteness index. * For the type of WG, the results showed no significant difference between the WG1 and WG2 types, in contrast to the WG3, which had a significant influence. In other words, the results show that there was no significant difference between the mean values of the whiteness index for the WG1- and WG2-coated types, and only the degree of whiteness of the WG3 type was significantly influenced at a \(p\) < 0.05 level. * The WG3 samples registered the highest values of the whiteness index. Regarding the relative light spectral reflectance measurements, Figures 5-7 show the different light spectra reflectance obtained for the three WG-coated types of samples. As it can be observed from these figures, all types of WG-coated tiles reached a minimum light reflectance in the range of 500-800 nm, which tends to increase through the rest of the visual range and then increases gradually in the NIR range. The region in the  
Figure 5: Specular light reflectance of the first set of specimens fired at 1000 °C during 20 min. Figure 6: Specular light reflectance of the first set of specimens fired at 1000 °C during 40 min. Figure 7: Specular light reflectance of the first set of specimens fired at 1000 °C during 60 min. range of 500-800 nm, which roughly corresponds to the visible range (yellow, orange, and red colors), is the one showing almost constant and minimum values of the relative light reflectance. Therefore, these values are the most interesting ones to look for differences between the behavior of the samples on the global light reflectance, and they were chosen to perform a series of ANOVA tests, whose results are shown in Appendix B. In this case, the aim was to determine if the spectral data are really influenced by the WG type of glass coating or the holding times of burning. From the nonparametric Mann-Whitney U tests for the specular light spectral reflectance in terms of the WG type of glass coating and time of burning shown in Appendix B, the following can be concluded:  
* There was a significant difference between all the types of WG coatings (WG1, WG2, and WG3) regardless of the holding time (\(p<0.001\)). * There was a significant difference between the holding burning times \"20 and 60 min\" and \"40 and 60 min\" of WG1 with \(p<0.001\). * There was no significant difference between the holding times \"20 and 40 min\" of WG1 with \(p>0.01\). * There was a significant difference between all the holding times of WG2 and WG3 with \(p<0.001\). * The WG3 type had the higher mean values, showing a greater reflection capacity compared to the other types. In summary, this proof of concept about the spectral reflectance values of the WG coating showed that the light spectral reflectance behavior is highly influenced in the spectrum range that extends from 400 to 800 nm for the composition of the three types of glass used in the WG coatings. The holding time of burning also had some influence, but it was much smaller in general, except in the WG1 type between the 20 and 40 min burning times, wherein no difference was reported.