A liquid with high surface wetting characteristics is applied to the surface of the part and allowed time to seep into surface breaking defects.

The excess penetrant is removed from the surface of the part.

A developer (powder) is applied to absorb the penetrant from the defect and create a background for viewing the results.

Visual inspection is the final step in the process. The penetrant used is often loaded with a fluorescent dye and the inspection is done under UV light to increase test sensitivity.

PT is probably the most widely used NDT method. The test object or material is coated with the visible or fluorescent dye solution. The excess dye is removed from the surface, and then a developer is applied. The developer acts like a blotter and draws penetrant out of imperfections which are open to the surface. With visible dyes, the vivid color contrast between the penetrant and the developer makes the "bleedout" easy to see. With fluorescent dyes, an ultraviolet lamp is used to make the "bleedout" fluorescent brightly, thus allowing the imperfections to be seen readily.