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Radiocarbon experts, however, rebuff both sets of charges. Choosing an unbesmirched area was one of the most important decisions they could have made at the time. Says anthropologist R. Ervin Taylor, director of the radiocarbon-dating lab at the University of California at Riverside: "If they sampled in the wrong place, then they were idiots--and I know that's not the case." Geoscientist Paul Damon, a member of the University of Arizona team that tested one of the 1988 samples, hastens to say that the swatch was selected conscientiously and on the advice of textile experts. Contradicting Adler, he maintains, "We stayed away from charring and what might have been charred." Beyond that, the samples were cleaned both mechanically and chemically to rid them of contaminants. In fact, charring per se does not alter an object's carbon 14 ratio: scientists routinely use the method to date pieces of charcoal.
A DECEPTIVE COAT OF VARNISH? One challenge to the radiocarbon dating that has received a good deal of publicity is that of Dr. Leoncio Garza-Valdes, a San Antonio, Texas, pediatrician with interests in microbiology and archaeology. In 1983, while examining a Mayan jade artifact that art experts claimed was a recent forgery, Garza-Valdes discovered that it was covered by a lacquer-like coating produced by bacteria. Since it also had traces of ancient blood on it that should have been datable by the radiocarbon method, he took it to the University of Arizona dating lab, where scientists scraped off a sample of this natural "varnish" as well as the blood underneath it. They came up with a date of about A.D. 400--definitely not modern, but still 600 years younger than the carving's style suggested.
Several years later, when the three labs, the University of Arizona among them, produced their wet-blanket dates for the Turin shroud, a possibility flashed through Garza-Valdes' mind. What if the shroud too had a "bioplastic" varnish--and the labs had been fooled into decreeing an object younger than it actually was? In May 1993 Garza-Valdes traveled to Turin, microscope in hand, and was put in touch with Giovanni Riggi, the microanalyst who had parceled out the 1988 samples. Riggi let Garza-Valdes examine a tiny piece of shroud that he assured him came from the same batch. Sure enough, Garza-Valdes discovered a bioplastic film. "I knew immediately that the coating was there," he says. Riggi gave him a couple of threads and a bloodstain sample to take home.
Two years later, working with microbiologist Stephen Mattingly of the University of Texas Health Science Center at San Antonio, Garza-Valdes determined that the coating was embedded with "coccal-shaped bacteria and filamentous mold-like organisms." In some places, the coating increased the diameter of the fibers as much as 60%--which the two scientists say could be enough to skew the radiocarbon dating by 1,300 years. What is more, this coating--which is transparent and thus invisible to the naked eye--cannot be removed by the conventional cleaning methods of most radiocarbon labs. Properly cleaned, says Mattingly, "I think you'd find out the [shroud's] linen is much older, though I don't know by how much."