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S C I E N T I F I C H I G H L I G H T S

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Revealing new insights into black stains on the passepartout of Leonardo da Vinci s Codex Atlanticus A combination of non-invasive measurements, micro-imaging and synchrotron spectroscopic investigations have revealed the composition of black stains that appeared on 210 passepartouts of Leonardo da Vinci s Codex Atlanticus, the most important collection of da Vinci s drawings. The Codex Atlanticus is one of the largest collections of Leonardo da Vinci s drawings and writings and is preserved at the Biblioteca Ambrosiana in Milan. The manuscript consists of 1119 original fragments or folii, each framed with a modern passepartout added by restorers to allow consultation of both sides of the documents. In 2006, greyish-black stains were discovered on approximately 210 of the passepartouts, around 1-2 cm from the folii, causing concern among curators and conservators. Microbiological research rules out any kind of microbial attack on the Codex as the origin of the dark stains. An extensive analysis has been conducted on Folio 843 of the Codex to better understand the blackening process. Non-invasive imaging measurements of the folio, micro-

imaging and synchrotron spectroscopy investigations of passepartout fragments at different magnifications and spectral energy ranges were exploited to examine the glued modern paper and the composition of the black stains. Micro-attenuated total reflection Fourier transform infrared (μATR-FTIR) imaging of fragments from the passepartout revealed the presence of a mixture of starch and PVAc glues, localised in the stained areas close to the margin of the folio. Field-emission scanning electron microscopy revealed that the black stains were concentrated inside spaces between cellulose fibres, where an aggregation of inorganic, roundish particles made of Hg and S were found.

Synchrotron-based X-ray fluorescence (XRF) mapping and X-ray absorption near-edge structure (XANES) spectroscopy experiments were carried out at beamline ID21. Macro and µXRF maps supported earlier findings from X-ray spectroscopy analyses, inferring the presence of Hg, S, Ca, Al, Cl, Si and K. Hg was detected mainly in the darkened region, while it was not detected in the region without alteration. A similar distribution was found for S, although it was also detected in the white regions. µXRF mapping of a stain showed a co-localisation of Hg and S that follows the shape of the dark stain (Figure 122a,b,d).

Fig. 122: a) Visible light image of the black stain region. b) RGB composite of µXRF maps of Hg (red), Cl (green) and S (blue) [step size (h × v), 4 × 4 μm; map size (h × v), 800 × 800 μm; ID21]. The magenta colour indicates the region where Hg and S signals overlap,

following the shape of the black stain. c) Macro-XANES spectra recorded at the S K-edge. Peak at 2.4737 keV corresponds to the sulfides (S-II), peak at 2.4777 keV to the sulfites (SIV) and peak at 2.4839 keV to the sulfates (SVI). d) Detail of RGB composite of µXRF maps of Hg (red), Cl (green) and S (blue). e) Selected area of interest for hyperspectral 2D µXRF maps at S K-edge. The RGB composite image

shows the distribution of sulfides (S-II) and sulfates (SVI) species.