Infrared and Raman Spectroscopy for the Analysis of Pictorial Materials: Leonardo da Vinci’s Last Supper in the Convent of Santa Maria delle Grazie, Milan †

This study presents the application of infrared (IR) and Raman vibrational spectroscopy to the analysis of the pictorial materials used in Leonardo da Vinci’s Last Supper, located in the Convent of Santa Maria delle Grazie in Milan. The research was conducted during the extensive restoration campaign led by Giuseppina Brambilla Barcilon between 1977 and 1999, in collaboration with Professor Giuseppe Zerbi’s research group at the Polytechnic University of Milan. A total of fourteen microsamples were taken from different areas of the mural to identify both inorganic and organic components through molecular-level spectroscopic analysis. Infrared and Raman spectra revealed the predominant presence of calcium carbonate as an inorganic support, along with organic materials such as shellac and beeswax, while synthetic polymers like polyvinyl-acetate and Paraloid B-72 appeared to be absent The results demonstrate that shellac, applied during Pelliccioli’s 1946 restoration, is the most ubiquitous material across all samples, and that organic binders have penetrated deeply through the painting’s stratigraphy, reaching the plaster layer. The study confirms the effectiveness of vibrational spectroscopy as a non-destructive diagnostic tool for documenting the chemical composition and restoration history of complex mural paintings.