Cleaning of two hundred year‐old copper works of art using citric acid with and without benzotriazole and 2‐amino‐5‐mercapto‐1,3,4‐thiadiazole

This paper studies the use of 5% (wt) citric acid without inhibitor, inhibited with benzotriazole (BTA) and 2‐amino‐5‐mercapto‐1,3,4‐thiadiazole (AMT) and de‐aerated with nitrogen in the cleaning of 18th and 19th century chalcographic plates. DC and AC electrochemical techniques have been used to characterize the effect of the inhibitors and to quantify the aggressiveness of the cleaning treatment. Citric acid removes copper surface tarnish. BTA and AMT inhibitors are similarly efficient. De‐aeration reduces corrosion to levels similar to those obtained with inhibitors.