This method detects surface and near-surface discontinuities in ferromagnetic materials by means of a magnetic field. When the part is magnetised, discontinuities lying perpendicular to the direction of the field create a magnetic flux leakage field at the surface (the field lines emerge from the surface of the part). This leakage field, and therefore the flaw, is revealed by ferromagnetic particles applied to the surface. Some of the particles are attracted by the leakage field and form a bridge across the edges of the discontinuity. These magnetically held particles outline the discontinuity and indicate its shape and size. A fluorescent material is usually mixed with the particles so that indications can be seen more easily under ultraviolet (UV-A) light.