Fluorescent Penetrant Inspection (FPI) is a kind of dye penetrant inspection that utilizes a specialized fluorescent dye to detect defects that could affect the quality, accuracy or integrity of precision cast parts. The dye, such as Fluorescent Zyglo®, is applied to the surface of a casting to reveal even the smallest defects. It is far more sensitive than other types of dyes. FPI is ideal for the high-quality surface finishes achieved with investment casting. In addition to being highly sensitive and a low-cost process, FPI work well for a wide variety of materials.