# A Multi-Analytical Approach to Investigate Fresco Paintings in a Hypogeum Environment
## 4 Discussion  
The multi-analytical protocol adopted here--relying exclusively on non-destructive techniques--yields critical information on both the pigment palette and the conservation state of the hypogeum frescoes in the San Pietro a Corte complex (Salerno, Italy), thereby giving conservators a sound scientific basis for future interventions. Thermographic and hygrometric surveys reveal a pervasive surface-moisture problem: relative-humidity values approach 100% in the central zones of the paintings. Such readings are consistent with the microclimatic conditions of this subterranean space, where high ambient humidity is readily absorbed by the porous plaster. Infrared reflectography revealed interesting technical and iconographic details of the representation not directly perceptible to the naked eye [36] (mainly due to high occurrence of saline efflorescences on fresco surface): the presence of a shading (attributable to a more elaborate execution) and signs of painting integration and restoration on the \"Madonna in trono con bambino fresco\" can be observed. The improved legibility of the figure of the [PERSON] could allow for comparative studies with other contemporary examples in southern Italy [17]. The results of the XRF analysis, carried out on the main colors of the representation (white, red, yellow, brown, green, and black), are in line with those reported in the literature for other medieval frescoes discovered in southern Italy [7; 17; 37; 38]: the palette is dominated by naturally occurring earth pigments--long prized for availability, chromatic range, and compatibility with the alkaline fresco technique [37]. Calcium (from the lime plaster) and sulfur (from both sulphate efflorescences and sulfation of paint layers) are ubiquitous. The white pigment shows a composition similar to that of the substrate; therefore, it has been identified as chalk, in line with data reported in similar literature studies [17; 37; 38; 39]. The only organic pigment found in this study is the black one that can be attributed to the use of charcoal black. The detection of iron, associated with its oxides and hydroxides, as the main element for the red, yellow, brown, and green colors, suggest the use of red and yellow ochres, burnt sienna and green earth [37; 40; 41]. Such earth pigments (red, yellow, brown, and green) were usually employed thanks to their complete compatibility for the fresco technique [42; 43]. \begin{table}
\begin{tabular}{c c c c} \hline
**Fresco Painting** & **Measuring Point** & **Main Element (Minor Element)** & **Assignment** \\ \hline \multirow{4}{*}{Madonna in trono con bambino} & Limestone & Ca (Fe, S) & CaCO\({}_{3}\) \\  & White pigment & Ca, (Fe, S, Sr) & Chalk (CaCO\({}_{3}\)) \\  & Yellow pigment & Fe, (Ca, S) & Yellow Ochre (limonite: FeO(OH) \(\cdot\)\(n\) H\({}_{2}\)O) \\  & Brown pigment & Fe, (Ca, S) & Burnt Sienna (limonite and hematite) \\  & Green pigment & Fe, (Si, Ca, S, K, Mg, Al) & Green Earth (silico-aluminates of Fe\({}^{2+}\)/Fe\({}^{3+}\)) \\  & Black pigment & Ca, S (Fe, Sr) & Charcoal Black \\ \hline \multirow{4}{*}{Teoria di Santi} & Red pigment & Fe (Ca, S) & Red Ochre (hematite: Fe\({}_{2}\)O\({}_{3}\)\(\cdot\)\(n\) H\({}_{2}\)O) \\  & White pigment & Ca (Fe, S, Sr) & Chalk (CaCO\({}_{3}\)) \\  & Yellow pigment & Fe, (Ca, S) & Yellow Ochre (limonite: FeO(OH)\(\cdot\)\(n\) H\({}_{2}\)O) \\  & Brown pigment & Fe, (Ca, S) & Burnt Sienna (limonite and hematite) \\  & Green pigment & Fe, (Si, Ca, S, K, Mg, Al) & Green Earth (silico-aluminates of Fe\({}^{2+}\)/Fe\({}^{3+}\)) \\  & Black pigment & Ca, S (Sr) & Charcoal Black \\ \hline \end{tabular}
\end{table} 
Table 1: Result of XRF analysis: elemental composition of the pigment from “Madonna in trono con bambino” and “Teoria di Santi”. As observed in other hypogeum contexts [7, 17], the inherent durability of these inorganic pigments has preserved the pictorial layers despite harsh environmental conditions.