Steve
Dye penetrant inspection (DPI), also called liquid penetrant inspection (LPI) or penetrant testing (PT), is an inspection method used to locate surface-breaking defects in all non-porous materials (metals, plastics, or ceramics). The penetrant may be applied to all non-ferrous materials and ferrous materials, although for ferrous components magnetic-particle inspection is often used instead for its subsurface detection capability. LPI is used to detect casting, forging and welding surface defects such as hairline cracks, surface porosity, leaks in new products, and fatigue cracks on in-service components.
In layman's term if you were to spray the area of the record which may or may not be cracked with liquid dye penetrant (luminous green in colour) and then inspect the area under ultraviolet light whilst using a magnification lens you should then be able to determine whether the record is cracked or not.
Dave