A multi-analytical approach for the study of red stains on heritage marble

Red stains on heritage marble, particularly those found on the Baptistery of San Giovanni in Florence, are primarily caused by minium (lead tetroxide) and lead (Pb), often concentrated between calcite grains. This discovery, supported by a multi-analytical approach including optical microscopy, X-ray fluorescence mapping, micro-Raman spectroscopy, and isotopic analyses, suggests that the lead originates from metallic items used during restoration campaigns between 1938 and 1944. The study also found that the Pb isotopic composition of the stains overlaps with data from Sardinian mines, further reinforcing this hypothesis. These findings provide valuable insights into the preservation challenges faced by cultural heritage sites and offer potential avenues for targeted conservation strategies.

Cantisani, E., Cuzman, O. A., Vettori, S., Chelazzi, L., Ciattini, S., Ricci, M., Manganelli Del Fá, R., Chiarantini, L., & Garzonio, C. A. (2019). A multi-analytical approach for the study of red stains on heritage marble. The Analyst, 144(7), 2375–2386. https://doi.org/10.1039/c8an02426j