The oil and whiting method used in the railroad industry in the early 1900s was the first recognized use of the principles of penetrants to detect cracks. The oil and whiting method used an oil solvent for cleaning followed by the application of a whiting or chalk coating, which then absorbed oil from the cracks revealing their locations. Soon a dye was added to the liquid. By the 1940s, fluorescent or visible dye was added to the oil used to penetrate test objects.
History of Liquid Penetrant
What is Liquid Penetrant?
Inexpensive and simple to use, the dye sprays in liquid penetrant testing can be applied to a variety of surface materials. This procedure is applicable to all sizes and shapes of both Weld and base materials for forgings, pipe and tubing, castings or other shapes and can be used for ferrous and nonferrous materials.