Chapter 3 Multispectral IR Reflectography for Painting Analysis Raffaella Fontana, Marco Barucci, Alice Dal Fovo, Enrico Pampaloni, Marco Raffaelli and Jana Striova 1 InfraRed Reflectography (IRR) 1.1 Fundamentals of IRR InfraRed Reflectography (IRR) is a well-established diagnostic technique for the analysis of paintings that consists in irradiating the painting with an IR source and in detecting the back-scattered radiation in a wide spectral band with a suitable device [1, 2]. Thanks to the transparency properties of most pigments to the infrared radi- ation, it allows the visualization of features underneath the painting’s surface (Fig. 1), such as the underdrawing (a preliminary sketch made by the painter on a preparation ground, prior to painting), the pentimenti (an underlying image in a painting pro- viding evidence of revision by the artist), subsequent retouchings or repaintings (generally speaking, foreign materials added at a later stage for modifying the art- work’s painting or structure), restoration intervention (the process of re-establishing the artwork legibility through selective removal of patina, consolidation of ancient materials and eventual reconstruction of missing pieces). The visibility of the underlying features depends on the paint layers’ thickness and chemical composition, as well as on the chemical composition of the materials that form both the under- drawing and the preparation. If the preparation layer is characterized by a high reflectivity in the IR spectral range (a typical case is chalk-and-gypsum-based preparation) and the underdrawing is carbon-based, the visibility of the preparatory sketch is evident, whereas it decreases in case of iron-gallic inks or sanguine. Paints’ transparency generally increases with the wavelength of the radiation used, reaching its maximum for most pigments around 1.7 micron. R. Fontana (&) Á M. Barucci Á A. Dal Fovo Á E. Pampaloni Á M. Raffaelli Á J. Striova CNR-INO, National Institute of Optics - National Research Council, Heritage Science Group, Largo E. Fermi 6, 50125 Florence, Italy e-mail: raffaella.fontana@ino.it © Springer Nature Switzerland AG 2018 D. M. Bastidas and E. Cano (eds.), Advanced Characterization Techniques, Diagnostic Tools and Evaluation Methods in Heritage Science, https://doi.org/10.1007/978-3-319-75316-4_3 33