## 3 Results
### Characterizations of the Coatings Applied on Raw Lecce stone  
Ten stones were coated by brushing them with the hydrophobic TP-Hy treatment; five of these were successively coated with the photocatalytic treatment N-TiA and five with P25. The amount of one application of TP-Hy hydrophobic and three applications of photocatalytic N-TiA or P25 was calculated from the weight difference after and before the applications: 2.2 \(\pm\) 0.5 mg/cm\({}^{2}\), 0.45 \(\pm\) 0.03 mg/cm\({}^{2}\) and 0.49 \(\pm\) 0.01 mg/cm\({}^{2}\) for TP-Hy, N-TiA and P25, respectively. SEM-EDS allowed us to investigate the surface microstructure and the elemental composition of _Lecce stone_ before and after the application of the TP-Hy/N-TiA and TP-Hy/P25 coatings. In Figure 4a, a secondary electron image of an untreated sample is reported. _Lecce stone_ is an organogenic carbonate stone, quite compact and characterized by a fine-grained structure. The granular stone structure made by clasts of micrometric size and by intergranular porosity is evident. Figure 4b-e shows the SEM measurements performed on treated stones. The EDS maps of Si and Ti show that the distribution of the coating is quite homogeneous, with small and rare aggregates of TiO\({}_{2}\) (Figure 4c,e) for both sols. Table 1 reports the elemental composition determined for the areas displayed in Figure 4a-c. The standards employed by the instrument are SiO\({}_{2}\) for Si, CaF\({}_{2}\) for Ca, SrTiO\({}_{3}\) for Ti, apatite for P and Fe\({}_{2}\)O\({}_{3}\) for Fe. The program automatically converts cation concentration to oxide concentration. All concentrations are expressed in oxide wt%. The abbreviation b.d.l. stands for below detection limit (approximately 0.1% wt). Because of the less-constrained geometry in analyzing areas, the obtained concentrations have to be considered semi-quantitative and are normalized to 100% for comparison among them. To verify that the treatments do not alter the original appearance of the stone, the total colorimetric variation \(\Delta E^{*}\) due to the application of TP-Hy/N-TiA and TP-Hy/P25 coatings was measured on the surface of the samples before and after the treatments. The results are summarized in Table 2, where the average colorimetric coordinates L*, \(a^{*}\), \(b^{*}\) taken at 27 points and the calculated \(\Delta E^{*}\) are reported. Figure 3: **(a)** Raman spectra of crystalline anatase and N-TiA nanopowder. The FWHM of the main peak is indicated by arrows; **(b)** XRD pattern of N-TiA nanopowder and crystalline anatase: (A) anatase; (B) brookite. In the N-TiA XRD, the fit (red line) to the main peak (at about 26\({}^{\circ}\)) is obtained by overlapping of contributions from A(101) (cyan line), B(120) (blue line), B(111) (pink line) and B(121) (green line) reflection planes. Figure 4: SEM image of untreated _Lecce stone_ (**a**), TP-Hy/N-TiA (**b**) and TP-Hy/P25 (**c**) _Lecce stone_, Si (**d**,**f**) and Ti (**e**,**g**) EDS maps. There are no evident changes in the aesthetic appearance of the coated stone surfaces. The color difference induced by both treatments is very low and lower for N-TiA than for P25. A slight yellowing (increase in the chroma coordinate \(b^{\star}\)) associated with a negligible decrease in luminance can be noted for the stones treated with P25. The values of the total color difference \(\Delta E^{\star}\) after the application of the TP-Hy/N-TiA and TP-Hy/P25 treatments are at the limit of the human eye perceptibility threshold, usually reported as \(\Delta E^{\star}\approx 3\)[7; 92]. Capillary rising is one of the most important mechanisms for water penetration into natural or artificial building materials and is the main cause of building degradation. The influence of the coatings on the behavior of raw stones against water was investigated through measurements of water capillary absorption before and after coating.