X-ray radiography allows for the investigation into the structure of paintings on wood panel and canvas, paper and cardboard. The values of the lights and darks on the plate are a function of the greater or lesser absorption of the radiation by the object under examination. In reading an x-ray plate, it is important to keep in mind – in addition to the thickness of the painted layers – that some pigments are very opaque and have a high atomic weight (in particular white lead). On the plate, the light and dark areas will be formed as a function of the resistance to the passage of the x-ray of the various parts of the object. In those areas were thickness’ are equal, the areas with greater density will appear lighter.