Advanced NMR methodologies and micro-analytical techniques to investigate the stratigraphy and materials of 14th century Sienese wooden paintings

Abstract In this study a multi-analytical approach was used to characterize ancient and modern constitutive materials and the stratigraphy of a Sienese wooden painting consisting of four cusps belonging to a lost Polyptych , by Andrea di Bartolo dated back to the late 14th century, repainted in the 16th century and partially restored and cleaned in the 20th century. In order to distinguish the original layers from the other ones, a comparison with the painting Adorazione dei Magi by Bartolo di Fredi (Andrea's father) dated to the 14th century, was performed. The painting Adorazione dei Magi was found to be in a very good state of conservation and provided a model of the artistic technique used in Sienese painting in the 14th century. In situ measurements by portable NMR were performed to investigate the stratigraphy of the paintings in a non-destructive and non-invasive way. By means of this technique, information about all layers constituting the paintings were obtained and used to plan the successive micro-sampling. High resolution NMR spectroscopy was applied on a few samples to characterize binders and organic substances. Specifically, solid state 13 C and 31 P CPMAS NMR spectroscopy and 1 H NMR spectroscopy in solution were applied to characterize original and non-original materials. Other techniques such as ToF-SIMS, HPLC, IR and Raman spectroscopy were also applied.