In magnetic particle inspection, what is the function of the indicating medium?

• A. To color the metal for easier visibility
• B. To clean the surface after magnetization
• C. To indicate the presence of flux leakage by forming visible aggregates
• D. To demagnetize the part after inspection

Answer: (C)

In magnetic particle inspection, the indicating medium’s job is to reveal where the magnetic field leaks at defects. When the part is magnetized, flux lines distort and leak at discontinuities like cracks. The iron-based particles in the indicating medium are drawn to those leakage areas and form visible aggregates, showing the location and shape of the flaw. This makes otherwise hidden cracks detectable under proper illumination. The medium isn’t intended to color the metal, to clean the surface, or to demagnetize the part—demagnetizing is a separate step done after inspection if required.