A promising approach to address this issue involves the application of low-cost and highly adaptable Reflective Microscopy (RM), which is well-suited to real corrosion conditions. Available in many configurations and known under multiple names (optical microscopy, time-lapse microscopy, twodimensional surface optical reflectance, spatio-temporal real-time optics, etc.), the basic principle remains the same: the registration of images of reflected light from an in-situ corroding metal interface. Despite these advantages, RM has historically found only a limited number of applications in the corrosion analysis, primarily related to passive film rupture events, such as spatial identification of pit locations, measurement of pit size and morphology, with interpretation based on the localisation of low-contrast reflected light regions. This limitation was due to the inability to convert the intensity of reflected light to quantifiable physical parameters, restricting analysis to semi-quantitative estimation of pit locations. However, our recent studies on Al6061 alloy, mild steel, and pure Fe substrates -and independently, research by other groups on Al2024 alloy, duplex stainless steel, and Ni-Cr-Mo alloy -have demonstrated that variations in reflected light intensity can be quantitatively correlated with surface film thickness via Fresnel equations, the same theoretical framework used in ellipsometry. Despite this advancement, the practical minimum thickness of reliably measured surface films remains in the range of a few nanometers, while passive film thickness on SSs can be in the sub-nanometer range, highlighting the need for further refinement to make RM a reliable tool for PSZ detection.