X-rays
with X-radiography. The X-ray film
is in the gold colored envelope behind
the painting; the grid on the panel's
reverse is a cradle. The green
cylinder is the X-ray tube.
X-rays are located on the spectrum between ultraviolet and gamma rays, and have a much shorter wavelength than visible light. Since materials absorb them to different degrees, X-rays are used to identify pigments, to reveal changes in the composition, and to study a painting's support and condition. Like visible light, X-rays affect photographic emulsions; when a painting's absorbency pattern is registered on film, the result is an X-radiograph.
X-ray films are used in sealed envelopes to protect them from exposure to visible light. To make an X-radiograph, the painting is positioned between the X-ray source and the film. To obtain an exact 1:1 image of the painting the film is placed against the paint surface.
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