X- Radiography

Detail: X-ray of Christ
X-radiography is one technique used by conservators to discern what lies beneath the surface of the finished painting. As in medical investigations, radiography reveals internal details buried inside the physical object. When radiation passes into an painting, some of it is absorbed, some is scattered and some may pass through the object. The amount that passes through depends on several factors, including the energy of the radiation, the composition and thickness of the object, the elemental composition of each paint layer, and the fabric or wood support. The heavier, denser elements in a paint layer block the x-radiation and appear lighter in on x-ray film. Consequently, flesh tones that contain lead white appear lighter than areas of landscape containing earth pigments from iron oxides. In paintings, certain clues may indicate that an artist made changes while working on a composition. Often the prominent texture of brushwork from an earlier image is discernible on the painting's surface. When a painting is x-rayed, the artist's initial ideas can be seen on the x-ray film. Here, for example, the contour of the sleeve of the robe of Jesus was formerly extended further away from his body.

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