Electron emission radiography
An imaging technique that uses electrons emitted from the object to form the image. In this examination technique, a mono-layer radiographic (or photographic film) is placed on top of and in close contact with the object because air gaps could deteriorate the image quality. The object and the film are then irradiated with high-energy x-rays (200 kV to 250 kV). The x-rays pass through the film nearly without being absorbed. When the x-rays penetrate the object, they are absorbed and the energy is reemitted as secondary electrons. The image is formed by these electrons that strike the film. Heavy elements have higher emission rates than lighter elements and thus the image relates to the elemental composition of the object's surface. The technique has been used for exmination of easel paintings, drawings with metallic inks, degraded stained glass, engraved metallic artefacts, wood panels or radio-opaque supports.