Figure 4

Cu-K edge XEOL-XANES spectra from RoIs shown in Figure 3 (b). Guided by the oxidation state image in Figure 3(c) regions of interest were set up on predominantly Cu(I) and Cu(II) areas. The RoIs are shown in Figure 3(b) and respectively numbered 1 and 2. RoI 1 comprises two separate Cu(I) areas. The spectra are shown with one from a pure copper reference at the same monochromator calibration. The data from both RoIs contains a shoulder at 8.983 keV which is probably characteristic of the underlying copper. Otherwise The green curve from RoI 1 is consistent with cuprite XANES, whereas that from RoI 2 (blue curve) shows a shift characteristic of tenorite. The presence of copper-related features suggests that the patina is <200 nm thick, or discontinuous. The reason for the arrowed pre-edge spike is not known.