Through the limelight: analysing the earliest collection of magic lantern glass slides in Portugal

The magic lantern, developed in the mid-17 ^th century, was the first optical instrument for projecting transparent images painted on glass slides. It became a powerful tool for scientific and religious education, entertainment, and advertising throughout the 18th and 19th centuries. This study presents the first multi-analytical characterisation of 20 hand-painted glass slides from the collection of the Science Museum of the University of Coimbra (Portugal). A predominantly in situ approach was employed, combining Micro Energy-Dispersive X-ray Fluorescence (μ-EDXRF) and Ultraviolet-Visible (UV-VIS), complemented by micro-sample analysis using Micro Fourier Transform Infrared (μ-FTIR) and Micro Raman Spectroscopies. The results provide insights into the materials and techniques used and enable an assessment of their conservation state at the microscopic level. By identifying different glass compositions and colourants, this study establishes correlations with historical written sources and comparable European slides, contributing to a better understanding of artists’ practices and supporting attribution and preservation decisions.