Grounded on these conclusions, we fitted maps of normalized optical intensities of the passive layer around areas where two pits later formed, assuming a bi-layered Cr 2 O 3 /Fe 2 O 3 structure with each layer being 0.2 nm thick (Fig. ). The normalized intensities (shown in Fig. and) exhibit very slight variations, ranging from 98.8 % to 99.4 %. Areas where pits eventually formed, at approximately 10 µm and 30 µm, show a slightly lower intensity of 98.8 % compared to the rest of the profile. It is important to note that these are not yet pits, as identical values of 98.8 % are also observed in other regions, visible as dark blue areas in Fig. , where no pits appear. These slight variations can be attributed to structural variations in the passive film. In this particular case, we attributed the locations of future pit formation to a depletion of Cr 2 O 3 (as shown in Fig. ). Numerical modeling under this assumption provided a good fit for the normalized intensity, as demonstrated by the overlay of our model with the experimental data in Fig. . The provided explanation suggests Cr 2 O 3 depletion in the passive layer in regions corresponding to blue clustered pixels in Fig. . This observation aligns with the literature, where passive film breakdown is often attributed to Cr 2 O 3 depletion. However, more detailed localized surface analyses, directly correlated with the optical signatures of passive layer formation, are still needed in the future to confirm this hypothesis. Furthermore, it is noteworthy that not all blue areas ultimately evolve into sites for pit formation. This observation suggests the presence of subtle differences within these clustered regions that are beyond the sensetivity of the optical microscope. These finer variations also warrant investigation through more sensitive surface analysis techniques in future studies.