This one of the NDT methods which is used widely in various industries. This method means of locating and determining the severity of surface discontinuities in the materials, based upon capillarity attraction.
Penetrant is applied to the surface of the specimen and sufficient time is allowed for penetration into the surface discontinuities. After removal of excess penetrant, developer is applied which acts as a blotter which draws the penetrant from discontinuity and the penetrant appears on the surface of the specimen as an indication.
This test is suitable for all material except porous material.
Which may produce confusion in results.