This diffusion during early stages of isochronal heating, and its role in the partial dissolution of iron oxide layers, is likely driven by the creation of new chemical phases and the generation of microdefects. To interrogate this hypothesis, we focus on selected m/z regions of mass spectra for the borate coating and the two oxide layers (Fig. ). These spectra were acquired within the temperature range 200-510 °C, capturing information about the dynamic formation of chemical compounds before reaching the glass transition temperature of sodium borate (~520 °C in vacuum, Fig. ). The borate coating showed clear signs of iron incorporation, with the detection of 56 Fe + above 200 °C. The intensity of this secondary ion gradually increased with temperature (Fig. ).