Introducing Chemical Vapor Etching (CVE): A Material-Selective Approach for Surgically Precise Tarnish Removal

The controlled removal of corrosion products is a persistent challenge in fields ranging from industrial alloy protection to cultural heritage conservation. Achieving high precision and selectivity in subtractive treatments remains difficult because of chemical complexity and structural heterogeneity of the corrosion layers. Inspired by the surface-chemistry principles of Atomic Layer Etching (ALE), we developed a vapor-phase strategy termed Chemical Vapor Etching (CVE), which is conceptually analogous to chemical vapor deposition operated in reverse. CVE is demonstrated on artificially corroded Cu-Sn-Pb bronze that simulates marine-aged artifacts. Using Hexafluoroacetylacetone (Hhfac) as a volatilizing agent, corrosion products, including oxides, hydroxides, carbonates, and chloride-containing phases, are selectively converted into volatile species and removed, whereas the underlying substrate remains unaffected. SEM and XRD confirmed the preservation of surface morphology and phase composition, whereas EDS/XPS revealed the efficient removal of sulfur species and strong reduction of chlorine. The process exhibits tarnish-limited, self-terminating behavior, with etching effectively ceasing once a stable Cu/Cu₂O interface is reached. By combining chemical selectivity, time-controlled removal, and non-line-of-sight capability, CVE provides a controllable alternative to conventional mechanical, laser, and plasma-based cleaning approaches. Beyond bronze conservation, this strategy offers a chemically precise route for managing corrosion in technologically relevant, copper-based systems.