X-ray

X-rays are a type of radiation which may be used for analysing aspects of a work of art not visible to the naked eye.

X-rays will pass through most solid objects, but are obstructed by some materials. The heavier the atoms of a substance, the more resistance to the rays. An X-radiograph records the areas of the work where the X-rays have been impeded; such parts appear white. Pigments containing heavy metals such as lead therefore show up, as do the nails used to construct an altarpiece.

X-radiographs are difficult to interpret because the image shows all of the layers of the work superimposed.