## 3 Results
### Epr  
CW-EPR was applied on two small fragments (SG35 and SG36) to evaluate if this technique could provide further information on specific aspects of the samples; EPR is able to spot paramagnetic defects (color centers, radicals) or paramagnetic metals (Cu\({}^{2+}\), Mn\({}^{2+}\), Fe\({}^{3+}\)), which are commonly present in many pigments and materials as substitutional ions. EPR is a bulk technique, so the whole sample is examined and specific pieces of information related to the different painted layers are not accessible.  
A preliminary overview of the two fragments, front and back, was conducted using optical microscopy and Raman spectroscopy.  
The SG35 front (Figure 9) is characterized by a layer with small blue grains on a yellow background giving a green hue. Some bigger blue grains can be spotted, which [PERSON] identifies unambiguously as azurite. On the back, pale green crystals are present, which [PERSON] identifies likely as a combination of brochantite (basic copper sulfate) and atacamite (basic copper chloride), which are likely alteration by-products from an original copper-based pigment. Two unidentified peaks at 444 and 1475 cm\({}^{-1}\) suggest the presence of some other compound.  
The EPR spectrum of SG35 (Figure 10) is characterized by a sharp signal, whose g-factor (g = 2.0035) is related to a C radical, likely a radical in C black. A six-line pattern is also observed, attributable to Mn\({}^{2+}\) in Ca carbonate, and a signal at g\(\sim\)2.06, with linewidth Hpp = 4.3 mT can be attributed to Cu\({}^{2+}\) in some compounds deriving from the alteration of a copper-based pigment. In azurite, brochantite, and atacamite (the copper-based pigments detected by Raman), the Cu\({}^{2+}\) ions are either antiferromagnetically coupled or have very broad EPR lines; therefore, the g\(\sim\)2.06 signal is unlikely to be related to these latter and could be attributed to some complex of copper with an organic compound.  
Figure 8: Sample SG39B: SEM-BSE image with associated SEM-EDS spectra from the spots indicated, and \(\mu\)-Raman spectra calculated on two different paint layers (actual analyses in red, reference spectra from mineral databases in blue).  
The SG36 front is uniformly covered by blue grains, which [PERSON] identifies again as azurite. The SG36 back is yellow-red on a white background; only peaks due to calcium carbonate are observed in the Raman spectrum.  
In the EPR spectrum of sample SG36, no Cu\({}^{2+}\) signal is observed, while a strong Mn\({}^{2+}\) six-line pattern is seen, again attributable to manganese in Ca carbonate. The signal is stronger than in SG35. The C black radical signal is also seen, although weaker than in SG35. Both SG35 and SG36 present a broad background signal attributable to iron oxyhydroxides.  
Figure 10: **Left**: EPR of SG35. Red asterisk marks the sharp signal of a C radical; blue arrows mark the sextet of Mn\({}^{2+}\); the red circle highlights the signal of Cu\({}^{2+}\). **Right**: EPR of SG36. Red arrow marks a C radical; blue arrows mark the sextet of Mn\({}^{2+}\).  
Figure 9: **Above**: SG35 front (**left**) and back (**right**). **Below**: SG36 front (**left**) and back (**right**).