## 3 Results and Discussion
### Laboratory Micro-Raman Results
As far as the blackish-brown and grayish areas (points S11, S12, S14, S16, S17, S18, S20) are concerned, Figure 8 reports two representative photomicrographs and corresponding \(\upmu\)-Raman spectra, collected on a blackish and grayish micro-fragments (sampled at point S11 and S12) of the painting, respectively. Figure 7: Photomicrographs, in white reflected light, and \(\upmu\)-Raman spectra collected on flesh-toned micro-fragments sampled at point S6 (**a**,**d**), S10 (**b**,**e**) and S22 (**c**,**f**) of the _“The Glory of St. Barbara”_ painting. Concerning the \(\mu\)-Raman spectrum of sample S11 (Figure 8c), it shows two major contributions centered at \(\sim\)1312 cm\({}^{-1}\) and \(\sim\)1567 cm\({}^{-1}\), associated with the \(D\) (disorder) and \(G\) (graphitic) bands of amorphous carbon. This result indicates the use by [PERSON] of a typical carbon-based black pigment of organic provenance. Unfortunately, an accurate identification of the carbon source cannot be accomplished through Raman spectroscopy. Nevertheless, considering the high concentration of Ca observed in the corresponding area through XRF and EPMA-EDS, several hypotheses can be still made. In particular, the detected amorphous carbon could be either of vegetal origin, such as vine black, usually attained by carbonizing plants or wood, or of animal origin, such as bone black (\(\sim\)85%: hydroxyapatite; \(\sim\)10%: elemental carbon; \(\sim\)5%: calcite and/or magnesium phosphate) or black ivory (\(\sim\)80%: calcite mixed with calcium phosphate; \(\sim\)20%: elemental carbon). In our case, the observation of a band falling at \(\sim\)959 cm\({}^{-1}\), associated to the stretching mode of the phosphate ion [PO\({}_{4}\)]\({}^{3-}\), along with the main peak of calcite at \(\sim\)1081 cm\({}^{-1}\), led us to conclude that the black pigment used was most likely of animal origin (bone black or ivory black), thus excluding any vegetal recipe for the black-brownish colorations [6, 7, 8, 10, 12]. The \(\mu\)-Raman spectrum of the grayish micro-fragment (sample S12, Figure 8d) seems almost similar to that of sample S11, with the only exception of the appearance of a well-visible peak at \(\sim\)1051 cm\({}^{-1}\) due to the presence of white lead. Accordingly, it is reasonable to assume that a mixture of an animal-based carbon black and white lead was probably employed for the preparation of the grayish nuances, following black discoloration procedures. Such a consideration is in full agreement with both the XRF and EPMA-EDS results, which revealed a similar elemental composition for both the blackish and grayish areas of the painting except for the Pb content, which was found to be higher in gray areas than in black ones. The aforementioned considerations are further validated by the fact that the application of a carbon-based black pigment, often in mixture with white lead or calcite, was already testified in other paintings by [PERSON], including the _\"Penitent St.  
Figure 8: Photomicrographs, in white reflected light, and \(\mu\)-Raman spectra collected on a blackish and grayish micro-fragment sampled at point S11 (**a**,**c**) and S12 (**b**,**d**) of the _“The Glory of St. Barbara”_ painting, respectively. [PERSON]\"_[6], the _\"Madonna of Sorrows\"_[6], the _\"[PERSON] defeating Evil\"_[9], the _\"Dinner of Emmaus\"_[7] and the _\"Conversion of [PERSON]\"_[13]. Figure 9 reports the collected photomicrographs and \(\upmu\)-Raman spectra of the blue pigmented micro-fragments (sampled at points S15 and S21), representative of the cerulean and light blue areas of the painting. The \(\upmu\)-Raman profiles revealed, as a main result, the characteristic bands of indigo (C\({}_{16}\)H\({}_{10}\)N\({}_{2}\)O\({}_{2}\)), centered at \(\sim\)545 cm\({}^{-1}\) and \(\sim\)1573 cm\({}^{-1}\). Indigo is an organic compound in the form of a dark blue crystalline powder usually attained from plants of the genus _Indigofera_ (typical of tropical regions) since the Middle Ages.