Benzotriazole (BTA) is an inhibitor molecule, commonly used to protect copper and copper-based archaeological artefacts from degradation processes such as the ‘bronze disease’. The aim of the present work was to study in details the inhibition mechanism of the BTA molecule on pure copper and copper–tin alloy (called CNR 128) by the surface-sensitive techniques (field emission SEM with energy-dispersive X-ray spectrometer and XPS). To perform this investigation, the typical corrosion products of the patina, including cuprite (Cu2O) and atacamite (Cu2Cl(OH)3) compounds, were grown on pure copper and CNR 128 alloy. The BTA molecule was then applied on the surface of the prepared samples, following the method that is commonly used in the conservation of artefacts in cultural heritage. During the analyses of pure copper substrate, it was revealed by XPS that BTA molecule favours the formation of Cu(I) species, when it is adsorbed on an atacamite-enriched surface. On the contrary, when BTA molecule is adsorbed on a cuprite-enriched surface, it is promoted the formation of Cu(II) species. Instead, for degraded CNR 128 alloy where atacamite or cuprite were the main component of the patina, XPS results showed that the chemical nature of the bronze surface is present Cu(II) oxidation state. Copyright © 2012 John Wiley & Sons, Ltd.