Artworks preservation considerations: physical and chemical non-destructive and micro-destructive solutions for a smart restoration - a case study

In the recent years, the conservation and preservation of cultural heritage has received a large amount of attention around the world. The increasing need for non-destructive investigations is a major issue, as sampling is often restricted in view of the value or the uniqueness of the object. However, the integration between non-destructive and micro-destructive testing offers the possibility of obtaining more information about one specific sample avoiding false alarms in the detection of subsurface defects. The object of this work is part of the Madonna con Bambino fresco (XIII century) located in the Piazza del Popolo at Fontecchio (L’Aquila, Italy). Currently, the fresco shows some deterioration signs due to humidity variations, salts crystallization and acts of vandalism. In addition, some damages linked to the 2009 earthquake that partially destroyed L’Aquila city and its surroundings can be seen to the naked eye. In particular, a character of the fresco that represents an Angel has been inspected using the following non-destructive testing (NDT) techniques: electronic speckle pattern interferometry (ESPI), infrared thermography (IRT), near-infrared reflectography (NIRR) and ultraviolet (UV) imaging. After the NDT analysis, three micro-samplings have been collected choosing three different colors of the character. The position of each sampling is also related to a signal variation in the raw thermograms. The micro-samplings have been inspected in laboratory by scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS) and Fourier transform infrared (FTIR) spectroscopy analysis in order to exclude the influence of the emissivity variation in the thermographic inspection. Moreover, several algorithms such as principal component thermography (PCT) and higher order statistics thermography (HOST), have been applied to the raw thermograms enhancing the quality of the final images. Splitting, subsurface cracks and overpaintings have been detected by this integrated method that can be considered useful in the art restoration.