Fluorescent Dye

The test object is coated with a solution that contains a visible or fluorescent dye. Excess solution is then removed from the surface of the object but leaving it in surface breaking defects. A developer is then applied to draw the penetrant out of the defects. With fluorescent dyes, ultraviolet light is used to make the bleed out fluoresce brightly, thus allowing imperfections to be readily seen . With visible dyes, vivid color contrasts between the penetrant and developer make "bleed out" easy to see. The red indications below represent a number of defects in this component.