The dye penetrant method of inspection is a nondestructive test for defects open to the surface. It may be used on such materials as aluminum, magnesium, brass, copper, cast iron, steel, stainless steel, carbides, stellite, certain plastics and ceramics. 

Of the four available methods to remove surface penetrant during the fluorescent penetrant inspection process, the hydrophilic post emulsifiable penetrant process (Method D) is used when tighter control of the penetrant process is desired.