Here, we apply TOF-SIMS with in-situ heating to track chemical transport (Fig. ) and phase formations during the hot corrosion reactions between sodium borate coatings and oxide scales present on the surfaces of metals. Inorganic glass coatings are often applied to steel, cast iron, or aluminum products to protect them from corrosion, oxidation, wear, and tear . These coatings comprise two primary constituents: glass-forming compounds (e.g., P2O5, B2O3, and SiO2) and network modifiers (e.g., Li, Na, and K). In practice, they significantly benefit hot metal forming processes by forming viscous and lubricating liquid-like melts at high temperatures that can protect the steel components from wear and oxidation . However, these melts can also cause undesirable hot corrosion attack and form hard precipitated spinel oxides (Fig. ), leading to material losses and complicating descaling processes. Sodium has been strongly implicated in hot corrosion reactivity of these glass coatings at high temperature , with its mobility hypothesized as the main factor in glass melts . While ab initio calculations support the experimental hypothesis showing the diffusion of sodium from the borate glass to the Fe2O3 surfaces at elevated temperatures , no direct observation has elucidated this mechanism. We now seek to unambiguously identify the role of sodium in glass coatings below their transition temperatures by direct, real-time observations. Figure presents a simplified schematic summarizing the results of in situ TOF-SIMS heating experiments applied to a protective glass coating on the oxide layers at the surface of stainless steel.