Medieval alchemy code made of lead: degradation issues and proposals for future conservation

The subject of this work is an alchemical code engraved on lead pages, stored at the State Archives of Florence. The code consists of nine pages on which it is reported an alchemical recipe book. The dating of the code is uncertain and some scholars dates it back to the middle of the fourteenth century. Little is known about its history and how it was preserved until the moment it was purchased by the Archive in 1859. The alterations and the presence of thick and heterogeneous corrosion patinas on the surfaces of the pages required restoration work. Completely non-invasive investigations were carried out to support this activity using both imaging and punctual techniques. At first, for each of the pages, images were acquired in visible light and with the optical microscope for the purpose of documentation, images in grazing light to highlight the morphological characteristics and images in fluorescence induced by UV radiation to identify the possible presence of organic materials or, in general, of substances that may present fluorescence phenomena. For the complete identification of the materials Fiber Optic Reflectance Spectroscopy (FORS), FT-IR in total reflectance modality (TR FT-IR) and SEM-EDS analyses were performed. X Ray Diffraction (XRD) to determine the mineralogical phases were also conducted. Crossing all the data collected it turned out that the prevailing materials on the pages of the code are hydrocerussite and anglesite, respectively a carbonate and a lead sulfate. There were also compounds of more complex nature that have developed as a result of the interaction with the environment of those elements present as an impurity in the lead used for the realization of the book. The fundamental purpose of these investigations was the characterization of the alterations in order to identify a conservative strategy suitable for the code for future conservation.