Dye penetrant testing is a non-destructive testing process used to detect weld defects. The process involves first thoroughly cleaning the weld zone of a part. A red dye is then applied to the area. The red dye has a very low viscosity and can get into very tiny voids and cracks. A special cleaner is then used to remove all visible signs of the red dye. Although the red dye may appear to have been cleaned away, small traces of the dye will be left inside any tiny pores or cracks in the weld. A white developer is then sprayed over the surface and allowed to react with the red dye. If there are any defects, the red dye will be absorbed into the white developer and show up as tiny red dots that are easily detectable against the white developer. Each step in this process is carefully timed to allow for proper reactions to take place.