Liquid Penetrant Testing or Penetrant Testing (PT) is one of the oldest and most widely used non-destructive testing method. The origin of liquid penetrant testing is generally attributed to the inspection of wheel axles in the railroad industry in the 1890s. It is considered an effective NDT method and capable of detecting very small surface breaking discontinuities that cannot be found by direct visual examination in various non-porous materials. It is well suited to the detection of all types of surface cracks, forging laps, surface porosity, laminations, hot tears, cold shuts and similar discontinuities in various product forms. Penetrant testing can be performed on magnetic and non-magnetic materials, metal or non-metals, ceramics etc but does not work well on porous materials. It is extensively used for the inspection of wrought and cast products of both ferrous and nonferrous metals, powder metallurgy parts, ceramics, plastics, and glass objects.