Cracking Assessment in The David by Michelangelo

In large marble statues, the weight and the shape sometimes thin and articulated give rise to high mechanical stresses in the material, especially in case of earthquakes or other vibrations. The stress state, in conjunction with the brittleness of the marble, can originate superficial cracks. The David by Michelangelo, one of the most famous masterpieces of Western art, is located inside the Galleria dell’ Accademia in Florence and presents surface degradation. In fact some cracks are visible in the tree trunk lying flat to the right leg and in the left ankle. This paper describes the work done by the Authors to analyse the cracking phenomena in the lower part of the statue. The aim of the research is to estimate the depth of the most relevant cracks in the tree trunk and in the left ankle. Starting from an accurate survey of the state of conservation of the surface of the statue, the diagnostic process is carried out by means of ultrasound method. This technique has several advantages in the analysis of art works: in fact, it allows to study surface degradation and cracks without damaging or altering the properties of the material. Before this application of the ultrasounds method, an intense experimental test campaign was carried out in the laboratories of the Facutly of Engineering of the University of Bologna, aimed to validate both the instrumental apparatus and the experimental procedures. The diagnostic process of the surface degradation of the David is part of a research program aimed at cracks monitoring and diagnostics, started more than two years ago.