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Despite recent technological advances, it is currently not possible to uniquely and noninvasively measure the micrometric thickness of pictorial layers in paintings. The presence of optically opaque materials (pigments) severely limits the detection capability, as it hinders the penetration of the probe's near-infrared radiation, typically employed for this purpose. In our previous work, we explored the possibility of using diffuse reflectance spectroscopy (DRS) to achieve stratigraphic information about painting materials. We showed that the thickness of pictorial layers can be quantified by the intensity of the spectral reflectance factor measured at a given wavelength in the infrared, i.e., an easily detectable spectral feature. In the present work, we extend the previously proposed method by applying multispectral reflectography to measure new ad hoc prepared pictorial samples and a mock-up simulating a Mondrian painting. We thus demonstrate that it is possible to obtain 2D and 3D stratigraphic maps of the pictorial layer over large areas with the same measurement time and spatial resolution as multispectral scanning reflectography. [ABSTRACT FROM AUTHOR]

Studying highly valuable and fragile Renaissance drawings requires a non-invasive contactless analytical approach. In this work, we study an early drawing by Raffaello Sanzio, one of the most important artists of the Italian Renaissance, realized during his stay in Florence (1504–1508). Our analyses aimed to reveal the features of the paper support significant for its dating, identify and map the drawing media to understand the artist's technical approach, and document the drawing condition with imaging and single-sited optical methods. Reflectance Vis–NIR multispectral imaging spectroscopy elaborated with False-Colour and Principal Component Analysis provided information about the paper support and the drawing media. Laser scanning micro-profilometry and Optical Coherence Tomography allowed revealing the superficial micro-scale features of the support. The chemical composition of the different drawing materials was characterized by μ-Raman spectroscopy, which provided also some evidence of the conservation history of the drawing. Integration of spectroscopic and imaging data shows that Raffaello used different dry drawing media (carbon-based and Pb stylus) to sketch the figure and then refined the details and shadows with iron-gall ink. The paper presents a methodological approach for the analytical examination of fragile paper artworks. [ABSTRACT FROM AUTHOR]

Nonlinear optical microscopies (NLOMs) are innovative techniques recently introduced in the field of cultural heritage for the non-invasive in-depth analysis of artworks. In this review, we report on the state-of-the-art of NLOMs on different artistic materials, i.e., varnish, glue, paint, wood, parchment, and metal, and we evaluate the potential and capabilities of NLOMs in comparison with other more established linear optical techniques. We also discuss the latest studies defining suitable measurement conditions and instrumental requirements for the safe and in situ application of NLOMs on real cases. [ABSTRACT FROM AUTHOR]

Optical techniques are routinely applied in artworks analysis to obtain structural, morphological, and compositional information on the examined object in a non-invasive way. However, the complex structure of paintings, which can be sketched as multi-layer systems often including non-transparent layers, can hamper the penetration of the optical probe, making the non-invasive sectioning particularly challenging. Recently, cutting-edge photoacoustic (PA) methods have been tested on painted mock-ups to overcome the above-described detection limit of pure optical techniques, giving promising results. In this work, for the first time, PA measurements were taken on a nineteenth-century painting. Using a multi-modal approach, the effectiveness of the technique in revealing hidden features and providing cross-sectional measurements was assessed in comparison with other well-established pure optical techniques, namely multispectral Vis–NIR reflectography, UV imaging, fibre optics reflectance spectroscopy (FORS), optical coherence tomography (OCT), and laser scanning microprofilometry. Data integration allowed highlighting the capability of each method, proving the effectiveness of the proposed multi-modal approach. This successful application of the PA method on a real case study paves the way for its introduction among the other non-invasive techniques for paintings analysis. [ABSTRACT FROM AUTHOR]