Codex Atlanticus yields new insights into Leonardo da Vinci's works

The interdisciplinary research group examined the phenomena and studied its nature and causes using a variety of non-invasive and micro-invasive analysis techniques under the direction of Lucia Toniolo, Professor of Materials Science and Technology at the Politecnico di Milano, according to Phys.

The Laboratorio del Libro Antico (Laboratory for the Restoration of Ancient Books) of the Abbey of Grottaferrata undertook a significant restoration of the Codex Atlanticus, which was given to the Veneranda Biblioteca Ambrosiana in 1637.

After the intervention, 12 volumes with 1119 folios were produced; each page contains a passe-partout with a panel that was inserted by the Grottaferrata restorers to frame Leonardo's original fragments.

The drawings are now each individually mounted on passe-partout and stored in acid-free boxes and folders. Politecnico's investigation started in 2021 with a preliminary prototype study on three drawings from a Codex that involved changing the passe-partout on folio 843.

Studies done in the past had ruled out the possibility that the stains were caused by microbial degradation processes. Starch glue and vinyl glue were discovered by Politecnico di Milano's investigation, which combined hyperspectral photoluminescence imaging, UV fluorescence imaging, and micro-ATR-IR imaging. These spots are precisely next to the border of the folio where the staining is most intense.

Study abstract:

This paper accounts for the diagnostic campaign aimed at understanding the phenomenon of black stains appeared on the passepartout close to the margins of Folio 843 of Leonardo da Vinci’s Codex Atlanticus. Previous studies excluded microbiological deterioration processes. The study is based on a multi-analytical approach, including non-invasive imaging measurements of the folio, micro-imaging and synchrotron spectroscopy investigations of passepartout fragments at different magnifications and spectral ranges. Photoluminescence hyperspectral and lifetime imaging highlighted that black stains are not composed of fluorescent materials. μATR-FTIR imaging of fragments from the passepartout revealed the presence of a mixture of starch and PVAc glues localized only in the stained areas close to the margin of the folio. FE-SEM observations showed that the dark stains are localized inside cavities formed among cellulose fibers, where an accumulation of inorganic roundish particles (∅100–200 nm in diameter size), composed of Hg and S, was detected. Finally, by employing synchrotron μXRF, μXANES and HR-XRD analyses it was possible to identify these particles as metacinnabar (β-HgS). Further research is needed to assess the chemical process leading to the metacinnabar formation in the controlled conservation condition of Leonardo’s Codex.