Dye penetrant testing and magnetic particle inspection are non-destructive testing methods used to locate surface-breaking defects in materials. Dye penetrant testing uses penetrant that is drawn into defects by capillary action, then a developer is applied to make defects visible. Magnetic particle inspection magnetizes ferromagnetic materials, then iron particles are attracted to leakage fields from defects. Both methods can detect surface defects rapidly and at low cost, but only work on appropriate materials and can only find surface or near-surface defects.