Figure 1: Showing the Cu 2p_3/2 (~932 eV) and the Cu_1/2 (~954 eV) peaks of a) a brass disc (BS002) has been cleaned (sonicated in micro 90 and water for 10 minutes), b) a brass disc (BS004) which had been corroded by fingerprint sweat for 24 hours and then cleaned, c) the same disc as in b) which was left in air for a further 15.5 hours d) the same disc in b) after being left in air for a further 65 hours. Data normalised so the Cu 2p_3/2 peaks are the same height.

One can see very little if any change over time. This is possibly due to the the use of micro 90 before taking the XPS spectra of sample BS004.