## 3 Results  
### SVV and HT Results  
The SPV and HT tests were performed on the frescoed walls of the apsidal conch of St. Panfilo's Church, selecting four areas characterized by fractures, infill of the underlying masonry, and near openings (doors and windows). For each panel, the SPV results are compared with the hygrometric one through maps obtained from data processing with GIS software. The point values have been interpolated to provide a 2D false-color map of the sonic velocity and hygrometric value distribution according to the Spline function. The maps in false color emphasize the different properties of the masonry and are shown in Figure 3.  
Figure 2: Example of passive thermography analysis used to identify the support wall texture. Stones with irregular shapes can be distinguished behind the fresco.  
Figure 3: SPV and HT value distribution maps of **(a,b)** Panel A; **(c,d)** Panel B; **(e,f)** Panel D; and **(g,h)** Panel E. The plaster fractures are highlighted in red.  
The sonic velocity of the walls ranges between 0 and 2500 m/s. In most cases, these values are related to the layer of painted plaster, thus being less representative of the underlying support masonry. False color maps highlight the different properties of the masonry. Higher velocity values correspond to well-cohesive plaster that is well-bonded to the masonry (areas from blue to purple in the maps), while lower velocity values indicate portions of detached or damaged plaster resulting from fractures (red areas).  
In Figure 3a, the average velocity is about 700 m/s. The red area on the lower right shows lower velocities, which is due to both the detachment of the plaster and a large discontinuity that starts from the right edge of the window and cuts the masonry.  
The HT values show that the humidity of the plaster increases towards the edge that delimits the conch area from that of the church naves (Figure 3b).  
In Figure 3c, the average sonic velocity (\(v\)) is around 600 m/s, while in the right portion, average velocity values of about 370 m/s are recorded. These lower values are mainly due to a detached portion of the plaster that is located in the central portion of the investigated area. On the left side, however, where the plaster shows good cohesion to the masonry, the velocity is higher (average of 850 m/s).  
In Figure 3d, the moisture values of the plaster are higher and more homogeneous (>20 WME%) than in the other areas investigated. This phenomenon is most likely due to the position of this area relative to the cardinal points; in fact, the wall is exposed to the sun only in the morning. The area corresponding to the detached portion of the plaster falls below 10 WME%, in accordance with SPV results.  
In Figure 3e, the average sonic velocity is around 370 m/s. This area is affected by widely detached plaster. Moreover, a discontinuity is visible that divides the opening frame, probably made from stone, to the masonry and brings a variation of velocity; the right part has a higher velocity than the left side.  
The results of the HT show that the moisture of the plaster increases going down (Figure 3f). In this area, the humidity value never exceeds 10 WME%, which can most likely be linked to the presence of numerous detached portions that allow air circulation. In addition, this wall of the conch communicates with the rooms of the rectory, so it is not directly exposed outside.  
In Figure 3g, the left portion has lower sonic velocity values. On the right side instead, the velocity is higher (1500 m/s on average). This separation is found in the correspondence of a discontinuity in the coating plaster, as well as in the masonry itself (highlighted in red in Figure 3g). Figure 3h illustrates the HT values recorded, which indicate an increase in the moisture of the plaster in the lower right portion.