Abstract 1-Phenyl-5-mercaptotertrazole (PMTA) was found to be more effective than chromate and other organic agents for protecting brass from tarnishing. A 5 min passivation treatment in 1.2 g dm −3 of PMTA solution at 30 °C formed a protective film on Cu 2O and ZnO. Based on X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) determinations, the film formed had a composition of 47.2% C. 20.6% Cu. 6.5% Zn. 12.7% N. 9.1% S and 3.9% O. It was deduced from differences in binding energies of N and S before and after film formation that N and S in the PMTA structure were coordinated with Cu + and Zn 2+ in the film.