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Abstract:

Ordinary x-radiography of a painting on metal is unsatisfactory because the x-ray absorption of the thin film of paint is negligible compared to the absorption of the metal plate. Electron radiography, however, used on such a painting, gave a good image, revealing a ruff collar and lace headdress which had been painted over. The technique is to place the film, emulsion side down, in very close contact with the paint surface, and to irradiate with high-energy x-rays through the film. These x-rays have only a small fogging effect on the film, but when they strike metallic pigments in the paint they cause electrons to be emitted which can travel the short distance to the film, and there register an image. An infrared exposure is shown for comparison. Details of a sample electron radiograph: 200 kilovolts at 10 millamps for 3 minutes. X-ray tube distance 1 metre. Film: Kodak Industrial X-ray film, Type M (Single-coated).. Filter 8 mm. copper. G. Thomson