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It certainly released a new wave of fascination, both popular and scientific. In the 100 years following Pia's epiphany, the cloth has been removed from its silver casket not just for the public but also to several waves of scientific observers. The trend's high point occurred in 1978, when the Roman Catholic Church allowed a five-day extravaganza during which more than two dozen scientists from the U.S., Italy and Switzerland performed a battery of tests on the shroud and also used pieces of tape to lift material from its surface for later study. The tests included photo- and electron microscopy, X rays, spectroscopy, ultraviolet fluorescence, thermography and chemical analyses. Among the scientists' findings: that the shroud had come into direct contact with a body and that the "blood" on the cloth is probably real blood. The figure itself bears no telltale brushstrokes and seems have been rendered by no artistic method either of the Middle Ages or of Jesus' time. Publicized by a spate of books, the 1978 findings exposed more people to the shroud than had ever thought of it before--and convinced a hefty portion of them that it was indeed Christ's burial sheet. That is, until an additional experiment seemed to rule out that possibility entirely.
On April 21, 1988, under the gaze of Anastasio Cardinal Ballestrero of Turin and a video camera, Italian microanalyst Giovanni Riggi cut a 1/2-in. by 3-in. strip of linen from the shroud, well away from its central image and any charred or patched areas. He divided the strip into three postage stamp-size samples and distributed them to representatives of laboratories in Zurich, Oxford and the University of Arizona in Tucson. Each then performed at least three radiocarbon measurements on its sample.
Radiocarbon dating works by measuring an artifact for an isotope called carbon 14, traces of which are contained in all organic substances, including the flax plants from which the shroud's linen was made. Carbon 14 is unstable and decays over time into another isotope. The amount present in living organisms remains nearly constant because it is continually replaced through the intake of food and air. But when animals and plants die, their level of carbon 14 begins to decrease at a known, fixed rate. Thus the amount of residual carbon 14 in an object provides a measurement of its age.
The scientists retreated to their labs. In October of the same year, the Oxford team gave a press conference at the British Museum. To eliminate suspense, they had helpfully written two dates on a chalkboard behind them: "1260-1390!" This estimated span for the origin of the shroud's linen was later detailed in an article co-written with the other two labs for the journal Nature, which straightforwardly stated that the radiocarbon-dating results "provide conclusive evidence that the linen of the Shroud of Turin is medieval." Nuclear physicist Harry Gove, who helped develop the radiocarbon-dating process used on the shroud, went a bit further. He said the odds were "about one in a thousand trillion" against the shroud's having been woven in the time of Jesus. Edward Hall, a member of the Oxford team, went further still. Anyone who continued to believe the shroud was genuine, he pronounced, must be a "flat-earther."