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This International Standard specifies a method of revealing pores or other discontinuities, when testing metallic coatings, that are not visibly affected by ferricyanide and chloride ions during the test period and that are cathodic to iron and steel. This method is especially useful for thick, hard chromium coatings used for wear resistance. NOTE 1 With some coating materials a very thin layer is dissolved by the sodium chloride solution during a 10 minute application period (see 5.2.3). The impact of such dissolution is that potential porosity, i.e. pores that have been covered over by very thin layers, are sometimes re-exposed. Experience has shown that such potential porosity is frequently re-exposed during actual service.