Joint Investigation with Ground Penetrating Radar and Infrared Thermography as a Diagnostic Support for the Restoration of Two Wall Mosaics in the Church of St. Mary of the Admiral in Palermo, Italy

Abstract

The church of S. Mary of the Admiral in Palermo, known as “La Martorana” and very famous for its Byzantine mosaics, has been a World Heritage site since 2015. The mosaic system of the church includes several groups of figures and scenes from the life of the Virgin Mary. From the western part of the ancient church only two mosaics survive, detached from their original position, and are now located in two internal chapels. On the occasion of several restoration works, these two mosaic panels were investigated with non-invasive techniques, in order to provide diagnostic support to the restoration and consolidation interventions. The investigations were aimed at detecting any air pockets that could cause the detachment of the tesserae or of possible differences between cement mortars under the tesserae. For this purpose, the integrated use of two non-invasive techniques namely infrared thermography (IRT) and ground penetrating radar (GPR) was considered. The joint analysis of IRT and GPR data allowed the interpretative uncertainties inherent in each technique to be reduced. Furthermore, for both techniques differentiated analyses were performed for layers at different depths under the mosaic surface. The results of these analyses were found to be more reliable regarding GPR data, compared to infrared thermography, the latter being more influenced by the reflectivity of the tesserae. However, the results partially confirmed the restorers’ diagnosis, also allowing the identification of further critical areas that could be affected by deterioration or compositional differences in the layers supporting the mosaics.

Graphic Reconstruction of a Roman Mosaic with Scenes of the Abduction of Europa

“…In order to reduce scale error, 21 Ground Control Points (GCP) with defined values x, y and z (Figure 6), were placed around the mosaic on the surface of the wall on which the mosaic is placed. The numbering of the points started in the bottom-left corner outside the mosaic and continued to the right in an anti-clockwise direction [33][34][35]. Each GCP was measured using Geodetic Total Station Leica TS09plus 5 ′′ (Leica Geosystems AG, Heerbrugg, Switzerland).…”

An HBIM Integrated Approach Using Non-Destructive Techniques (NDT) to Support Energy and Environmental Improvement of Built Heritage: The Case Study of Palazzo Maffei Borghese in Rome

“…Finally, researchers have focused their attention on specific aspects of the study of historical buildings, such as wall stratigraphy, the conservation of wooden floors or the supporting walls of paintings and mosaics [74][75][76][77][78][79][80][81].…”

Virtual three-dimensional model of the subsoil of the church of St. Maria Maddalena d'Alga in Palermo, using high-resolution GPR surveys

“…II. GPR SURVEYS Ground Penetrating Radar (GPR), commonly called georadar, is today a consolidated method that is widely used for diagnostics and research in archaeological prospecting and in other fields of cultural heritage [4][5][6][7]. In this field, the success of GPR is mainly due to its characteristics of high resolution within the first meters of depth [8], high acquisition speed [4], high integrability with other nondestructive methods [9][10][11][12][13] and, finally, high detectability of anthropogenic structures [9,14].…”