This International Standard specifies two low voltage tests for detecting and locating defects that extend to the basis metal in vitreous and porcelain enamel coatings. Method A (electrical) is suitable for the rapid detection and determination of the general location of defects. Method B (optical), based on colour effects, is suitable for the more precise detection of defects and their exact locations. Method A is commonly applied to flat surfaces, whereas method B is preferred for more intricate shapes. NOTE 1 Selection of the correct test method is critical to distinguish the areas of increased conductivity detected by method B from actual pores that extend to the basis metal, which can be detected by both methods. NOTE 2 The low voltage test is a non-destructive method of detecting defects (see clause 3) and therefore, is completely different from the high voltage test specified in ISO 2746. The results of high and low voltage tests are not comparable and will differ.