test method that use an oil solvent for cleaning followed by the application of a chalk coating, which absorbed oil from the cracks revealing their locations, and a dye is adde to the liquid, katsemeetod, mille korral kontrollitava pinna puhastamiseks kasutatakse õlilahustit, järgneb kriidipulbriga katmine, mille tulemusel õlilahusti absorbeerib pragude asukohad ning vahel lisatakse õlilahusele ka värvaine