It turned out what is happening with the documents of Leonardo da Vinci: they began to change

The Codex Atlanticus is one of the most extensive and fascinating collections of Leonardo's drawings and writings.

da Vinci.Its conservation is a big problem for scientists and researchers. Employees of the Polytechnic University of Milan studied sheet 843 of the Code in order to understand the origin of some of the black spots on the document. They appeared a few years ago on a modern passe-partout binding Leonardo's original folios.

An interdisciplinary research team used a range of non-invasive and micro-invasive methods of analysis to study this phenomenon, its nature and causes.

Codex Atlantean given by VenerandaThe Biblioteca Ambrosiana was restored in 1637 at the Laboratorio del Libro Antico of Grottaferrata Abbey between 1962 and 1972. In the end, the experts produced 12 volumes with 1,119 sheets: each page has a mat with a panel (added by restorers in Grottaferrata) framing original fragments of Leonardo's documents. Since 1997, the Code has been stored in a strictly controlled environment, in accordance with paper conservation standards.

In 2006, experts noticed that the documentsVinci began to change: very small black spots were found on the passe-partout, located around the panel framing and binding the folio. They were found on about 210 pages of the Code, starting with folio 600. This caused great concern among museum curators and scientists. In 2009 several volumes were divided.

Today, drawings are individually mounted onpasse-partout, in folders and boxes made of acid-free cardboard. The study, carried out by the Polytechnic Institute, began in 2021 during the work on replacing the Passepartout sheet 843.

Previous studies have ruled out that spotsarose as a result of microbiological spoilage processes. Employees of the Politecnico di Milano conducted hyperspectral photoluminescence imaging, UV fluorescence imaging, and other observation methods. In the end, they found traces of starch glue and vinyl glue in places where the staining was particularly intense.

In addition, scientists noticed the presence of roundinorganic nanoparticles with a diameter of 100-200 nanometers, consisting of mercury and sulfur. They accumulated in the cavities formed between the cellulose fibers of the passe-partout paper. Finally, synchrotron analysis at the ESRF in Grenoble identified these particles as metacinnabarite, mercury sulfide in an unusual black crystalline phase.

Black spots on the passe-partout of folio 843 of the Codex Atlanticus. Credit: Polytechnic University of Milan

In-Depth Research on Conservation Methodspapers made it possible to formulate some hypotheses for the formation of metacinnabarite. The presence of mercury has been linked to the addition of anti-vegetative salt to the adhesive mixture used in the Grottaferrata restoration technique. It was applied only to certain areas of the passe-partout paper in order to prevent microbiological contamination of the Codex.

Nanoparticles composed of mercury and sulfur on sheet 843 of the Atlantic Code. Credit: Polytechnic University of Milan

The presence of sulfur, on the other hand, causedair pollution (in Milan in the 1970s SO2 levels were very high). Perhaps it's the additives that were used in the glue. Over time, this would lead to a reaction with mercury salts and the formation of metacinnabarite particles responsible for the appearance of black spots.

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Cover photo: folio 843 of the Codex Atlanticus
Credit: Codex Atlanticus, Veneranda Biblioteca Ambrosiana, Milan