MT is used to identify surface and subsurface lacks in ferromagnetic materials. Magnetic particles can have a fluorescent pigmentation (visible in dark environment by the use of UV rays) or contrasted colours (visible with white ambient lighting).
At lacks, the magnetized object presents an outwards deviation of the magnetic force lines that forms a dispersed flow. Lacks become evident spraying surfaces with an adequate suspension of ferromagnetic, colorful or fluorescent powder. The accumulation of this powder allows the identification of any possible lack.