Integrating Legacy and Contemporary pXRF Data for the Compositional Characterization of Obsidian: Towards Robust Inter-Instrument Comparative Analysis

Obsidian is a non-crystalline volcanic silicate glass that played a major role in human technological development from the Paleolithic onward, owing to its brittle fracture and ability to produce sharp cutting and scraping edges. From the Upper Paleolithic, its long-distance circulation enabled the reconstruction of ancient exchange networks through the identification of geological sources. This study evaluates the non-destructive elemental characterization of obsidian using handheld portable energy-dispersive X-ray fluorescence (pXRF), with emphasis on compositional variability, analytical reproducibility, and inter-instrument comparability. Two pXRF spectrometers, the Thermo Niton XL3t GOLDD+ and Bruker Tracer 5, were assessed for precision, consistency, and robustness under standardized analytical conditions. A reference dataset comprising twenty-three archaeological obsidian fragments attributed to Aegean geological sources, Thira/Santorini, Melos, Nisyros, and Giali, was analyzed using both instruments. Statistical comparison demonstrated strong agreement in the clustering and discrimination of samples according to geological source, although differences in absolute elemental concentrations were observed, reflecting instrument-specific calibration procedures and measurement parameters. The results highlight the importance of standardized calibration using reference materials, rigorous quality control, and comprehensive methodological documentation for reliable interlaboratory comparison. Overall, handheld pXRF provides a reliable non-destructive approach for volcanic glass characterization and supports the development of transferable and reproducible datasets for silicate solid materials.