Segni e colori nel telaio del tempo: tracce, luce e materia nella policromia della Sardegna. Contributo alla conoscenza e conservazione di dipinti murali romani e medievali

This research project, starting from the lack of information of the wall paintings technique in Sardinia, has reconstructed the pictorial palette and the artistic techniques used in the late Roman and medieval times. An integrated analytical protocol (XRD, μATR-FTIR, SEM-EDS) was carried out in order to characterize pigments, binders, degradation and restoration products. The roman wall paintings technique in hypogeum environments in Cagliari widely used a proteinaceous material as additive, so that they cannot be considered made with a fresco technique. Egyptian Blue, red, yellow and green earths have been detected. The stratigraphic observation has revealed the presence of a tonal foundation for the drafting of Egyptian Blue, red and yellow earths. Undocumented restorations have been discovered. It is conceivable that in medieval wall painting technique in Sardinia lime and an organic material as binder were employed. The hypothesis that a proteinaceous material, such as casein, now totally mineralized, would have given origin to a widespread presence of calcium oxalate in the pictorial stratigraphy has been advanced. Lapis, red, yellow and green earths have been detected. It is not excluded that the investigated wall paintings lost the finishing layers because of detachments or excessive cleanings in restorations. A tonal foundation for Lapis and green earth has been detected as well as the presence of restoration products; compatibly with the restoration reports acrylic resins could have been used. The research project also investigated the colour system as a potential strain of a new discipline, the "symbolic History", in order to investigate how the perception of colours in a given historical period has been reflected in pictorial techniques, in the choice of the colours and pigments influencing the material consistency of the wall paintings. As a final point, the thesis deepened the mechanisms and tools of the collaborative knowledge as opportunity to review the polychrome apparatuses according to this new perspective. This research project is therefore designed as an analytical investigation on polychromy and wall painting techniques used in Roman and medieval times in Sardinia, in a vision that transcends the purely analytical methodology in order share and expand the knowledge to the general public and in the scientific community.