**2. Materials and Methods**

Table 1 reports the samples. Since most of the samples had clearly different overlapping color backgrounds, when possible without risk of contamination, the individual layers were separated with a scalpel and analyzed individually. Fragments of the eight most complex samples were analyzed as polished cross sections. From each fragment, the support mortar layer was taken and characterized.

**Table 1.** Description of the samples, identified pigments and employed analytical techniques (OM: optical microscopy; FTIR-ATR: Fourier-transform infrared spectroscopy in attenuated total reflection; XRD: X-ray diffraction; SEM-EDX: scanning electron microscopy-energy dispersive X-ray spectroscopy; PCS: polished cross section).




