A non-invasive methodology for stratigraphy investigation of historical violins using reflection IR spectroscopy and UV induced fluorescence technique

In the Cultural Heritage field, the stratigraphic analysis is carried out through the study of cross-sections [1]. This methodology is fundamental to discriminate the different layers composing a work of art, but it necessarily implies invasive sampling or micro-sampling with the consequent loss of precious or unique fragments. For this reason, the possibility of sampling is denied most of the time, especially in the case of historical musical instruments of the likes of Stradivari and Guarneri violins. Having been played during the centuries, these great masterpieces have undergone different kinds of degradation and wear, and subsequent invasive restorations. As a consequence, varnish layers have been thinned or even removed from the surface in different areas and other materials could have been added overlaying the original ones, with a variation in the coating thickness over time. This research presents a preliminary non-invasive methodology aimed to identify the stratigraphy of historical stringed musical instruments, by characterizing the different layers of original and retouching varnishes as well as wood treatment materials. A combined analysis was carried out using reflection infrared spectroscopy and UV induced fluorescence (UVIFL) photography. Firstly, an experimental study on laboratory models reproducing musical instrument stratigraphy was performed. Different thicknesses of varnish covering wooden samples treated with proteinaceous material and silicates, carbonates and sulphates were considered in order to assess the sensitivity of the method. Subsequently, the procedure was applied to five historical violins hosted in the Museo del Violino in Cremona (Italy), as shown in Figure 1. The stratigraphic results allowed to build up the knowledge about the construction techniques used by ancient violin makers.