CT investigation of "La Muta" by Raffaello Sanzio

In non-invasive diagnostics of paintings, the X-ray imaging is an important resource to acquire significant information on the state of conservation of support and pictorial surface. To this aim, generally, the radiographic technique is enough to fulfil the most part of these needs. However, there are particular cases where a tomographic investigation is needful to obtain information on the inner part of the support [1]. In fact Computed Tomography (CT) allows overcoming the main limitation of radiography: the overlapping of all depth levels in the resulting image, giving no information in the direction parallel to the propagation of X-rays beam. CT allows obtaining cross-sections of the object, the so-called "slices", which represent a faithful density map of each point in the considered section [2]. The painting so called "La Muta", made by Raffaello Sanzio around 1507, is an oil on wood (64 × 48 cm2) that represents a woman portrait. It is considered among the best examples of Raffaello’s portraiture of early maturity [3]. The painting, kept in the Galleria Nazionale delle Marche at the Palazzo Ducale in Urbino, is currently located at the Opificio delle Pietre Dure (OPD) in Florence to be subjected to restoration. Before starting the intervention, some diagnostic tests have been performed, including an X-ray radiography, which has showed the presence of many galleries in the wooden support due to Xylophages insects. However, the radiographic technique does not show the depth level of the tunnels for assessing whether they can eventually cause damage to the paint layer. This type of information, very important to preserve the pictorial surface, has been obtained using the CT investigation. The acquisition has been performed using a transportable tomographic system at the OPD and the data set has been processed in order to present an immediate and accessible result to the restorers for the next phase of consolidation of the painted surface. The CT investigation on the Raffaello’s masterpiece has been carried out in the framework of a collaboration between the INFN-CHNet network and the OPD. In this work, the transportable CT system and data processing are described.