Material density and its thickness set the limits of RT’s usefulness. Internal flaws are RT’s forte; its two dimensional views sometimes its drawback. RT uses penetrating radiation and works on the principle that denser or thicker materials will absorb more radiation and a sheet of radiographic film or image amplifier. A flaw presents anywhere within the specimen will absorb less radiation than the specimen itself. The flaw’s presence and location will be indicated by an area of higher or darker exposure.