Establishing a quantifiable tarnish timeline for comparison of anti‐tarnish processes in metals

Abstract

Brass samples were controllably tarnished using the thioacetamide accelerated corrosion (ISO 4538:1995) and synthetic sweat (ISO 3160-2:2003) methods. Spectrophotometry, energy dispersive X-ray spectroscopy (EDX) and electrochemical impedance spectroscopy (EIS) were performed on samples tarnished for set exposure times over seven days. Synthetic sweat produced a loose surface corrosion layer, which limited the use of EIS and spectrophotometry, but for the thioacetamide method both measurements produced a continuous change over the time period. EDX was able to observe a continuous change in the surface layer chemistry for both methods over the whole timescale and represents the best characterisation method to establish an equivalent tarnish timeline against which anti-tarnish treated samples can be compared. The current study was conducted using brass, however the method can be used for quantifying tarnish on other metallic systems.