Most people are familiar with the use of X-radiography in hospitals. The same principles apply to the use of X-rays in a museum, though we may use longer exposures to penetrate metals and other dense materials.
It is a useful tool to the conservator as it can helps us discover ‘hidden’ constructions and mechanisms, which we otherwise couldn’t see. It can be used to consider the extent of deterioration of an object or to check whether a firearm is loaded. A major advantage of this technique for use on objects is that it is entirely non-destructive.
X-rays form part of the same electromagnetic spectrum that includes radio waves, ultraviolet and visible light. However their greater energy compared to visible light allows them to pass through much denser materials.
Light can be stopped by a couple of pieces of paper whereas X-rays, if their energy is sufficiently high, may penetrate several centimetres of steel.
The X-ray beam, however, will be partially absorbed by the object and the intensity of x-rays passing through denser parts will be most strongly reduced.
Photographic film is sensitive to X-rays and a sheet of this is placed below the object being examined. After developing the film, the less exposed areas corresponding to denser parts, will appear lighter. The completed X-rays are scanned to produce digital images for use in reports and presentations.
This gun has suffered from insect damage and the weakened wood of the stock has been filled with an adhesive to strengthen it. The adhesive has a higher density than the wood and so the extent of the woodworm damage is visible on the x-ray.