Copper Discoloration: Correlation Between Copper Oxidation States and Their Colors

Here we report a novel approach on how to differentiate the copper oxidation state based on their colors. A series of analyses are carried out in order to determine the correlation between the state of copper oxides and their colors by using X-ray photoelectron spectroscopy (XPS). Our analysis results reveal that the light and dark brownish colored copper areas are formed by different copper oxide compositions whereby dark colored copper area consisted a mixture of Cu₂O and CuO, whilst the light colored copper area is dominated by Cu₂O with trace of CuO.