Non-invasive advanced investigation of Leonardo’s mural painting in Sala delle Asse

Sala delle Asse is a renowned hall in the Falconiera Tower in Castello Sforzesco commissioned by Ludovico il Moro, who entrusted its decoration to Leonardo da Vinci. The walls and the ceiling of the room were decorated at the end of the 15th century with mural paintings representing interlaced trees. The decoration was whitewashed and forgot for centuries but, during the 19th and 20th centuries, the painting was rediscovered and restored twice, uncovering the remnants of original layers. Starting from 2013, new conservation works were planned by Ministry of Culture, aiming at restoring a correct legibility of the decorations. To develop the conservation best practice, an in-depth study of the materials applied on the room surfaces is in progress. Recently, an advanced non-invasive approach was used, combining micro-XRF mapping, Raman spectroscopy and remote hyperspectral imaging systems (400-2500nm), which allowed investigating also the inaccessible parts of the panting such as the ceiling (Figure 1a). The selected areas under analysis included both cleaned and uncleaned portions in order to identify the pigments used for the original painting and the subsequent restorations. Moreover, pigments distribution was visualized via chemical images, permitting a preliminary reconstruction of layers superimposition (Figure 1b and 1c). The results obtained on this prestigious case study enrich the knowledge about Leonardo’s technique used on Milanese wall paintings.