# A Multi-Analytical Approach to Investigate Fresco Paintings in a Hypogeum Environment
###### Abstract  
In recent decades, there has been an increase in the development of non-invasive and non-destructive analytical techniques in the field of cultural heritage. The present study aims to characterize the frescoes in the hypogeum environment of the San Pietro a Corte complex in Salerno (Campania, Italy) through a multi-analytical approach that couples Infrared Reflectography with X-Ray Fluorescence Spectrometry. Thermographic and hygrometric measurements were also performed to evaluate their state of conservation in relation to environmental parameters such as relative humidity and temperature at the frescoed walls. Spectroscopic investigations revealed a predominant use of natural pigments--chiefy iron-rich earths--and uncovered details invisible to the naked eye that aid art historians in refining stylistic attributions. Hygrometric data showed that the central zones of the frescoes retain the highest moisture levels, underscoring the need for a carefully tailored conservation plan. Overall, this multi-analytical methodology provides important information that enables conservators and restorers to understand both the materials and the preservation requirements of these artworks from a scientific and conservation perspective. cultural heritage; X-Ray Fluorescence Spectrometry; non-invasive analysis Article  
The SPC complex has been the subject of recent studies due to problems related to the conservation of these frescoes, exposed to phenomena of salt crystallization and efflorescence [2; 3]. It is well known that the main factors in the deterioration of stone materials and wall paintings located in enclosed spaces are temperature excursions, water and humidity [4; 5; 6], soluble salts [7; 8; 9; 10; 11], and microorganisms [12; 13; 14]. High humidity values over long periods of time cause alternating cycles of hydration and dehydration, which, in the presence of soluble salts, lead to solubilization and recrystallisation phenomena, resulting in an increase in pressure within the material to the point of damaging part of its structure [15]. In the SPC hypogeum, saltpeter efflorescences of a biological origin were found, probably due to the infiltration of wastewater from nearby houses [2]. The high humidity of the air found in the complex and the presence of water infiltrations make the conservation of its works of art very difficult. In fact, the signs of degradation due to these phenomena are clearly evident: frescoes are completely covered by salt efflorescences as shown in Figure 2 (for comparison the red square highlights the area of the fresco that has been cleaned with a soft brush). From a stylistic viewpoint, these frescoes, dating back to the mid-twelfth to thirteenth century AD, have a pictorial matrix related to Byzantine culture. Although medieval artists generally had access to a wide palette, the hues employed in mural painting were necessarily more restricted: the alkaline wall matrix (usually slaked lime with sand or ground marble as fillers) is too aggressive toward most organic pigments, limiting painters to inorganic colorants [16]. Consequently, accurate identification of materials and techniques is critical for selecting appropriate restoration treatments and for devising preventive\(-\)conservation strategies [17; 18; 19]. Because the frescoes are already in a fragile state, the study relies on non-destructive analytical methods, now widely favored in cultural-heritage research precisely to avoid additional damage [20; 21; 22]. Rapid progress over the past decade has expanded the range and sensitivity of such techniques [23; 24; 25; 26; 27; 28; 29]. Portable instrumentation is particularly  
Figure 1: Location of the frescoes inside the hypogeum (from left to right): “Madonna in frono con bambino” in yellow, and “Teoria di Santi” in green. valuable: it allows for in situ characterization of raw materials and decay products, and pinpoints areas suitable for micro-sampling when laboratory study is indispensable [30,31].