X-rays
In archaeology these are used to examine the interiors of things that are difficult to see because of corrosion. In the conservation of iron objects, for example, X-rays are employed to see what is inside a rusted mass. Occasionally, previously unnoticed details of swords, knives and so on are seen on X-rays, including constructional and decorative features not visible on the outside. In such cases, archaeologists can judge whether the careful removal of the corrosion will be worth the effort. See also Radiography.