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Convinced he had picked up a forger's scent, Noble made tests to determine the specific gravity of the horse, found it was too low for solid bronze but about right if the statue had a sand core, held in place by iron wire and tacks—which is how French bronze statues in the 1920s were cast. Ordinary X-ray equipment would not penetrate deeply enough to show the interior of the sculpture. But on Sept. 15, Noble, using equipment developed to inspect the six-inch-thick steel hulls of nuclear submarines, was able to have a gamma-ray shadowgraph made. "They held up the film dripping wet, and for the first time I could see inside the horse," he says. "I could see the sand core, the iron wire and the iron points. That was it."