Fluorescent Penetrant Inspection (FPI) is a process for inspecting the surface of metals and other non-porous materials for defects (cracks, pits, etc.) that may compromise the integrity of a part, using a fluorescent liquid that fills the defects and then illuminates them under black light. FPI is a simple yet effective method, yielding high value for low cost. While limited to detecting surface defects, it is highly sensitive and able to identify even the smallest imperfections.