Dye penetrant testing, also known as liquid penetrant testing, is a type of nondestructive testing (NDT) method used to detect surface-breaking defects in a wide range of materials, including metals, ceramics, and composites.

The test is performed by applying a liquid penetrant to the surface of the material being tested.

The penetrant is allowed to seep into any surface-breaking defects, such as cracks or pores, and is then removed from the surface. A developer is then applied, which draws the penetrant out of the defects and creates a visible indication that can be easily seen and evaluated.

This method is commonly used to inspect metal parts, such as welds and castings, for defects that could affect their strength and performance.