## 2 Materials and Methods
As both FORS and XRF are non-destructive techniques, it was possible to acquire several spectra in different coloured areas for each tile, and also to repeat the measurements in some areas of the same colour on different spots. As far as physically possible, efforts have been made to perform the measurements on the same spot with the two techniques (XRF and FORS) also considering that the dimensions of the investigated areas are slightly different for the two methods. A total of 32 spectra were acquired by both XRF and FORS. All the areas analysed were documented by a portable digital microscope with 25\(\times\) magnification (Scalar DG-2A, optical zoom 25-200X, magnification @ 25X, field of view 13 \(\times\) 8 mm). Guided by the results achieved during the non-destructive survey, 12 micro-samples plus a whole fragment of a tile with gilding (split in two and labelled FED_13a, b) were taken from the terracotta and from the gilded tiles, in order to perform micro-destructive analyses to help interpret data obtained by non-destructive analyses and characterise the stratigraphic sequence and the composition of the materials. The number of samples was limited to avoid further damage to the monument due to its great historical value. Among the listed samples, five were devoted to reconstructing the stratigraphic sequence and obtaining information about the manufacturing technology of the gilded tiles. In Figure 2 is shown the image of the Federighi Monument with an indication of the sampling areas and the labels used to identify the tiles, listed in Table 2 along with the sample description and the applied analytical techniques. X-ray powder diffraction (XRPD) was employed using a Philips X'Pert PRO in order to determine the mineralogical composition. A copper anticathode (I = 1.54 A) was used with the following settings: current 30 mA, acceleration voltage 40 kV, explored 20 range between 3 and 70\({}^{\circ}\), step size 0.02\({}^{\circ}\) and stepping time 50 s. The XRPD analyses were performed on the terracotta samples and on the mortars. Morphological and semi-quantitative microchemical analyses were obtained by means of a scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS) ZEISS EVO MA 15 with a W-filament equipped with an analytical energy dispersion system from EDS/SDD, Oxford Ultimax 40 (40 mm\({}^{2}\) with a resolution of 127 eV @ 5.9 keV) and using the Aztec 5.0 SP1 software. The SEM/EDS measurements were performed on carbon coated cross sections of the samples with the following operative conditions: an acceleration voltage of 15 kV, 500 pA beam current, working distance between 9 and 8.5 mm; 20 s live time at an acquisition rate of at least 600.000 ct s\({}^{-1}\) on a Co-standard, processing time 4 for point analyses; 500 us pixel dwell time for maps acquisition with 1024 \(\times\) 768 pixels resolution. The software used for the microanalysis was an Aztec 5.0 SP1 software that employs the XPP matrix correction scheme developed by [PERSON] and [PERSON] in 1991 [27]. This is a Phi-Rho-Z approach which uses exponentials to describe the shape of the \(\varphi\) (\(\rho\)z) curve. XPP matrix correction was chosen because of its favourable performance in situations of severe absorption such as the analysis of light elements in a heavy element matrix. The procedure is a \"standard-less\" quantitative analysis that employs pre-acquired standard materials for calculations. The monitoring of constant analytical conditions (i.e., filament emission) is archived with repeated analyses of a Co metallic standard. LA-ICP-MS was performed using a CETAC LXS-213 G2 equipped with a NdYAG laser operating at the fifth harmonic at a wavelength of 213 nm. A 50 \(\upmu\)m circular aperture was used. The shot frequency was 20 Hz. A line scan was performed with a scan speed of 20 \(\upmu\)m s\({}^{-1}\) and was c. 250 s long following a 10 s gas blank. The helium flow was fixed at 600 mL min\({}^{-1}\). The laser operations were controlled by the DigiLaz G2 software provided by CETAC.