Fig. 2

SEM images in Backscattering Electron mode (BSE) of a selected area of the Pb-bearing glass grain indicating the dendritic etch features (black) within the glass matrix (white); the location of the extracted FIB section is indicated with a white rectangle; b image combining the BSE image shown in a with SEM–EDS chemical distribution maps for Fe (green), Pb (blue) and Si (red); areas depicted in lighter pink represent the unaltered Pb-silicate glass matrix whereas areas in darker pink depict Si-enriched alteration areas; the location of the remnants of a Zn-rich magnetite crystal in the extracted FIB section is encircled; c scanning TEM (STEM) images in bright field mode (BF) of the entire extracted FIB section; the orientation of the FIB section relative to the area from which it was extracted is indicated with red lines; the remnants of a Zn-rich magnetite crystal shown in b is encircled; the location of the areas shown in the Figs. 3a, e and 4a are labelled accordingly