*2.4. X-ray Fluorescence (p-XRF)*

Portable X-ray fluorescence (p-XRF) analysis was performed at MoMA with a Bruker Tracer III-SDD handheld XRF instrument with an Rh excitation source and silicon drift detector (5 mm diameter approximate spot size) under He purge. The instrument was operated at 40 kV and 3 μA, and spectra were acquired for 120 s. An Elio spectrometer (XGLab) equipped with an Rh target and 1 mm beam size was used for the analysis at MNAM. An integrated CCD camera and two laser pointers allowed precise focus on the region of interest. All analyses were performed in atmospheric conditions, with no He purge, at 40 kV and 100 μA, with a collection time of 200 s. All the spectra were examined with the Bruker Artax 7.2 software.
