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1 5 1 I H I G H L I G H T S 2 0 2 3
PRINCIPAL PUBLICATION AND AUTHORS
Imaging and micro-invasive analyses of black stains on the passepartout of Codex Atlanticus Folio 843 by Leonardo da Vinci, N. Guarnieri (a), M. Ghirardello (b), S. Goidanich (a), D. Comelli (b), D. Dellasega (c), M. Cotte (d,e), E. Fontana (f), L. Toniolo (a), Sci. Rep. 13, 4902 (2023); https:/doi.org/10.1038/s41598-023-31129-2 (a) Department of Chemistry, Materials and Chemical Engineering, Politecnico di Milano, Milan (Italy) (b) Department of Physics, Politecnico di Milano, Milan (Italy) (c) Department of Energy, Politecnico di Milano, Milan (Italy) (d) ESRF (e) Laboratoire d Archéologie Moléculaire et Structural (LAMS) CNRS UMR 8220, Sorbonne Université, Paris (France) (f) Veneranda Biblioteca Ambrosiana, Milan (Italy)
Macro-XANES spectra acquired at the S K-edge (Figure 122c) exhibited a remarkable difference between darkened and non-altered areas, both in signal intensity (high in dark, low in white region) and sulfur oxidation states (mainly sulfates (SVI) and sulfites (SIV) in white, also sulfides (S-II) in the dark region), suggesting a predominant formation of sulfides associated with the blackening (Figure 122e). Through the collective access Historical materials BAG , high angular resolution X-ray diffraction (HR-XRD) measurements were collected at beamline ID22 on samples from the dark and white regions, and μXRD experiments were carried out at beamline ID13. Thanks to these observations, the spatial distribution of the black stains and metacinnabar (β-HgS) peak heights could be correlated (Figure 123).
The research highlighted evidence of the spontaneous formation of β-HgS particles in conservation conditions (i.e., controlled environmental conditions including absence of light and low humidity). A first hypothesis about Hg provenance is based on the possible use of anti- vegetative mercury salts (HgCl2) in the gluing mixture. However, it is important to stress that this compound was not found throughout the current research. Additionally, it remains to determine if paper hydrolysis and the degrading processes of the glue mixture revealed by ATR- FTIR imaging may have contributed to the blackening phenomenon. Further studies are required to propose a formation mechanism for β-HgS and to verify if the exposure of HgCl2 to different sulfur sources, in mild environmental conditions, could lead to the formation of metacinnabar black particles.
Fig. 123: a) HR-XRD patterns of the white (grey) and dark (black) regions (ID22). Squares and diamonds highlight the peaks related to cellulose and β-HgS respectively. b) Visible light photograph of the area of the dark sample where µXRD mapping was performed. c) µXRD images calculated by integrating XRD intensity over regions of interest of XRD pattern, shown as green and purple rectangles in (a) for cellulose and metacinnabar respectively (ID13).
