The ISO 4623-1 standard specifies a method for determining the resistance of Paints and varnishes to filamentous corrosion performance on steel substrates. Filamentous corrosion is a localized form of corrosion on the metal surface under coating under humid conditions, usually manifested as a thin filamentous sign of corrosion under coating. The standard helps determine the Stability and durability of coatings in long-term use by simulating the actual use environment and evaluating the corrosion resistance of coatings. The standard details the test conditions, operating procedures, evaluation of results and scoring methods to ensure the accuracy and repeatability of test results.