Radiographic Testing involves the process where radioactive rays are directed at the object to be inspected, to pass through it and the resulting image is captured on a film. This film is in-turn processed and image displayed as a sequence of grey shades between black and white.
With Radiographic Testing the material is exposed to a homogenous ray from a radioactive isotope or an X-ray tube, while a negative film is positioned behind the material to be examined. After development of the film, thickness and density differences (I.e. material imperfections) will show as blackness differences. Acceptance criteria define whether or not the indication is non-acceptable (a defect) or not.