From tiny to immense: Geological spotlight on the Alexander Mosaic (National Archaeological Museum of Naples, Italy) using non-invasive in situ analyses

A key challenge in the art and archaeological field is the instrumental analysis of objects and materials while preserving their integrity. In this study, the world-renowned artwork Alexan- der Mosaic (The Issus Battle, collection of the National Archaeological Museum of Naples, IT), the most iconic representation of the face of the Macedonian king Alexander the Great coming from a Pompeii domus, was thoroughly analyzed with mobile and non-invasive meth- ods, within a great project of restoration started in 2020. Representative areas of the Mosaic, overall consisting of ca. two million of tesserae, was studied by in situ videomicroscopy, infra- red thermography (IRT), multispectral imaging, portable X-ray fluorescence (pXRF), Fourier transform infrared (FTIR) and Raman spectroscopy. Ten tesserae colors were discrimi- nated, and hypotheses on their geological provenances are proposed. Plasters, mineral components and other substances of old protective materials were characterized. The infor- mation obtained with this approach paved the way to knowledgeable restoration.