News Analysis

Is it time for new tests on the Turin Shroud?

Scientists are calling for fresh tests on the Turin Shroud after a paper challenged a previous finding that it dated from the Middle Ages. The paper, which queried the methodology of a 1988 study, has led researchers and scientific commentators to say it is “high time” for a new round of tests.

The Shroud, a piece of bloodstained linen imprinted with the figure of a man, is venerated by many as a precious relic: the burial cloth of Christ. Sceptics argue that it is merely a clever forgery.

Both sides can point to research supporting their case. In 1981, the Shroud of Turin Research Project team encouraged belief in its authenticity when they concluded: “The Shroud image is that of a real human form of a scourged, crucified man … not the product of an artist.” They wrote: “No chemical or physical methods known … can account for the totality of the image.”

But the case for authenticity would soon receive a strong challenge. In 1988, the Vatican allowed three labs under the aegis of the British Museum to carry out radiocarbon dating on the Shroud. The researchers published their findings in the journal Nature, and declared the Shroud to be of medieval origin – suggesting that it was indeed a fake.

The radiocarbon dating has been disputed by other researchers. It’s been suggested, for instance, that sample contamination or medieval repairs might have distorted the results. Yet the details of the 1988 tests have been hidden from view – until now. In 2017, four researchers obtained access to the data thanks to a freedom of information request. Their findings, published in the journal Archaeometry, raise questions about the precision of the 1988 calculations. The researchers – T Casabianca, E Marinelli, G Pernagallo and B Torrisi – call for fresh radiocarbon tests.

They argue that the variability in results from the subsamples indicates that the test samples cannot be considered representative of the Shroud as a whole. They conclude that new, rigorously planned testing is needed to establish a more reliable date.

The researchers’ call for fresh radiocarbon analysis has been echoed by other experts. Professor Walter Kutschera, former head of the Institute of Isotope Research and Nuclear Physics at the University of Vienna, said that recent advances make it easier “to extract genuine carbon material from a variety of different materials”. He believes “it is now possible to perform 14C measurements with a few micrograms.” This means researchers could “take samples from several places across the Shroud of Turin”, ensuring “a reasonable chance to obtain a good average age of the cloth”.

In radiocarbon dating, scientists determine the age of an organic artefact by measuring its level of 14C, a carbon isotope that decays over time. Professor Marian Scott of the University of Glasgow said that some variation in radiocarbon results is normal, “given the nature of any complex measurement process”. However, she added, sampling must be representative, “not preferentially selected from a specific area”.

For a relic like the Shroud, sample decontamination is key, according to Dr Liam Kieser, director of the radiocarbon lab at the University of Ottawa, Canada. “It has been handled by many people over the ages,” he said. “One would be concerned about the effect of finger oil.” He pointed out that the Shroud has survived several fires, “and while one can clean off smoke damage… the organic vapours associated with fires can also be absorbed and become more permanently embedded.”

Professor Timothy Jull of the University of Arizona, who participated in the 1988 radiocarbon dating, said that if the 1988 radiocarbon levels are in doubt, “the answer to that is to remeasure them if you want to do that”. But he has reservations about “vested interests” who “want the age [of the Shroud] to be more interesting.”

Another Shroud sceptic who is sympathetic to fresh testing is Professor Marco Bella of La Sapienza in Rome.
He commented: “There is a point in which I agree with the authors: we could repeat the radiocarbon determination. New techniques have better resolution, so we could better define the date in which the Shroud of Turin was made. It will definitively be again medieval, but if people still want to confirm that, I have nothing against it.”

Some researchers believe that fresh tests would not help. Dr Peter Steier, a radiocarbon expert at the University of Vienna, said he had heard credible reports of how repairs to the Shroud might have affected the 1988 results. But he was opposed to new measurements and believed that “scientific evidence” is “not suited to convince believers of any side.”

However, Philip Ball, an editor of Nature who helped to publish the original radiocarbon results, said a refusal to make new tests could look like “fear of what further studies might reveal”. Writing in Chemistry World last month, Ball said it was “high time for a fresh round of studies using state-of-the-art techniques”. He added: “Given the secrecy and reticence that has generally surrounded scientific investigation of this object, it’s no surprise that rumours abound of how the findings have been untrustworthy.”

The decision to test the Shroud will lie largely with the Vatican – who may be reluctant to submit the Shroud to more tests. Prof Kutschera said that he had proposed new tests to the Vatican in 2003 and 2007, but neither proposal was accepted.

If new tests are performed, Prof Kutschera said, there “must be an agreement between the scientists and the Church that the result will not be made public before a thorough discussion between these two authorities.”