Tarnishing and pitting corrosion mechanisms revealed by nanoparticles on the gold foil of Western Han Dynasty in Taiyuan, Shanxi, China through a multi-analytical approach

To figure out optical and corrosion mechanisms of tarnishing and pitting corrosion of the archaeological gold foil, ESEM-EDS, XRD, XPS were used to obtain chemical composition of different depths and observe surface topography. The results show Ag is enriched on the surface, mainly as Ag2O nanoparticles, and Au is enriched internally, due to the selective corrosion of Ag. Optical mechanism of gold tarnishing is surface plasmon resonance (SPR) of Ag2O nanoparticles. The colour darkens as nanoparticle size increases. Flaming in the atmosphere results in the accelerated oxidation of Ag and edge-off, leading to electrochemical crevice, pitting corrosion and perforation during burial.