Immediately after polishing and cleaning, the SS 316L plate was fixed at the bottom of a custom-made cylindrical electrochemical cell. The total area of the SS 316L surface exposed to the NaCl electrolyte measured 50 mm 2 , whereas only 1 mm 2 of this area was examined using an optical microscope. The SS 316L sample served as the working electrode (WE). Above it, a circular platinum net and a leakless 3.4 M Ag/AgCl electrode were placed, serving as the counter (CE) and reference (RE) electrodes, respectively. The electrochemical experiments were conducted using a CHI 660A potentiostat. The electrochemical cell was then placed into a RM setup, where both light illumination and collection occurred from the top (Fig. ). A detailed description of this setup has been previously documented elsewhere . In brief, the system incorporated an Olympus microscope, fitted with a water immersion objective (magnification ×10, 1.00-NA, Olympus LUMPlanFLN W) with a focal distance of ca. 3.5 mm. Imaging was achieved with an SVCam exo541MU3 CCD camera (SVS-Vistek GmbH, 4496×4504 pixels, 16 bit) operating at 10-25VDC. To enhance the camera's acquisition rate, binning was employed, reducing the resolution by a factor of 2 in both x and y dimensions. This adjustment resulted in an individual pixel size of approximately 0.48 µm. A halogen white lamp, filtered to produce = 490 nm blue light using an interference filter (with a spectral bandwidth of 20 nm), was the primary light source. The substrate received top illumination from this blue light beam via the microscope objective. The same objective then collected the reflected light, directing it towards the CCD camera, enabling real-time imaging of the light flux reflected by the analyzed surface. Before initiating the electrochemical experiment, the planarity of the SS 316L surface area was ensured (with a precision of 10 -2 • ). This was achieved using an interference Mirau objective (magnification ×10 (CF Plan, Nikon)) by minimizing the interference fringes over the imaged plane. After confirming the surface planarity, 20 ml of NaCl solutions at neutral pH and varying NaCl concentrations (5 mM, 10 mM, 30 mM, 50 mM, and 100 mM) were introduced into the electrochemical cell. Simultaneously, image acquisition commenced at a frequency of 5 Hz. After adjusting the focus of the optical microscope, we applied a cathodic polarization of -0.4 V vs 3.4 M Ag/AgCl for 40 s. Subsequently, we left the sample to rest at its open circuit potential (OCP) for 40 s. This procedure was designed to reduce the naturally formed surface layer through cathodic polarization and then to allow the layer to reform at the OCP (FK's comment : "and what if the pits are predetermine by the pristine state and by the polarization?" skipped). This approach improved reproducibility of the experiments. After that, a constant potential of +1.6 V vs 3.4 M Ag/AgCl was applied for 3 min. The precise value of the potential was selected based on preliminary tests within the range of 0 V to +1.8 V vs a 3.4 M Ag/AgCl. This was to ensure that pit formation was rapid enough to observe the dynamics of pit formation within the 3-minute duration of the experiment, yet slow enough to monitor the dynamic growth of the pits at an image acquisition rate of 5 Hz. All experiments exhibited consistent trends (vide infra), confirming their validity. Repeated trials at 10 mM and 30 mM NaCl further demonstrated reproducibility.