In-situ laser ablation MC-ICP-MS of lead white in paintings

This study develops and validates an in-situ LA-MC-ICP-MS method for lead isotope ratios (LIR) measurements of lead carbonate pigments at the micrometre scale. Two matrix-matched synthetic lead whites (PDLW1 and PDLW2) were produced from metallic lead, converted to carbonate, and characterised by solution MC-ICP-MS to define reference isotope compositions. These pigments were then used as calibrants and quality-control reference materials to assess LA performance, which yields accurate isotope ratios consistent with solution data. LA analyses on samples previously analysed by solution in other studies agree with the literature data. The analysis of mock-up cross-sections shows that oil-rich, pigment-poor domains degrade signal stability and precision, whereas pigment-rich domains provide accurate LIR, proving that this approach is valid to analyse LIR of paint samples. The method successfully identified the provenance of an anonymous sample believed to be a 16-17^th century Italian painting. Finally, LA was used to produce isotopic maps that resolve layer-specific LIR.