# The Characterization of a Fragment of a Medieval Fresco from Corbii de Piatra Cave Church
## 4 Conclusions  
Considering the advanced degradation of the whole fresco mural painting in Corbii de Piatra cave church, including the significant detachment of large portions of the fresco due to the friable mortar and small areas with high adhesion to the sandstone wall, this study aimed to characterize an element with high adhesion in the fresco and to establish correlations with factors that contribute to the stability to the fresco. The analyzed fresco sample was collected from an area with high adhesion on the northern wall of the church, which has the highest humidity due to water infiltration through the sandstone. The research facilitated the identification of the structural constituents, the determination of the elemental composition for the supporting mortar and the red painting layer, the identification of the inserts and their role in the propagation of cracks, and the identification of compaction defects in the fresco layers. The red paint layer appears to be continuous and unaltered, with an uneven thickness. It adheres well to the mortar support and, in some areas, appears to have penetrated the pre-existing cracks in the mortar. On its surface, a thin layer of carbonation, thick layers of deposits, and areas of surface degradation were identified. The roughness of the surface shows that the method of application was brushing. The pigments used for the red color in the pictorial layer were identified through X-ray diffraction and EDS elemental analysis as cinnabar (HgS) and red iron ochre (Fe\({}_{2}\)O\({}_{3}\), hematite). These compositions are consistent with those discussed in the work [4]. A mixture between the two pigments could also have been used. The DRX qualitative phase analysis highlighted the presence of calcium carbonate (CaCO\({}_{3}\)) and calcium and magnesium carbonate (Mg\({}_{0.03}\)Ca\({}_{0.97}\))O\({}_{3}\) in the mortar. The thickness of the intonaco mortar layer is uneven and varies between 15 and 41 \(\upmu\)m. The layer's characterization using OM and CL allowed the identification of the structural and petrographic constituents that originated from the mortar's preparation as well as from the dissolution/deposition processes under the action of meteoric water. The straw inserts identified by the carbon residue in the mortar are well integrated into the matrix, and the quality of the insert-mortar interface is good. The tips of the inserts are tension concentrators, from which cracks start. The cracks identified in the mortar are short. Some of them develop perpendicularly to the surface of the fresco due to repeated wetting/drying processes, while others occur inside the fresco. Part of the cracks originates from the top of the straw inserts. Rounded separations of fatty matter with yellow-orange light separations, were identified both in the mortar matrix and near the compaction defects. These separations may be deposits or may be associated with the addition of sheep tallow, a component used at that time to increase the quality of the mortar. The presence of moldic and vacuolar secondary pores was observed in the mortar, in canal-like spaces. The pores are large, irregular, and interconnected, allowing the infiltration/circulation of meteoric fluids in the lower layer of the fresco and thus reducing the advanced action on the upper layers. Mortar and pigments, the materials identified as being used for the fresco, are of indigenous origin. The quality of the mortar matrix and the formation of an interconnected network of pores that allow the circulation of meteoric fluids in the mortar layer of the fresco without degrading or detaching the mortar can explain its good adhesion to the sandstone wall. In this situation, the mortar behaves as a drainage mortar. Previous research led to the testing of a mortar with a similar composition.