For the past 600 years Christians have venerated the Shroud of Turin as a precious relic, a portrait of Jesus, and (perhaps) even proof of the reality of the resurrection. Then, in 1988, three laboratories based at top universities performed radiocarbon analysis of some of its threads. The results were collected and collated by the British Museum in London and published in a splashy article in the prestigious Nature magazine that claimed to offer definitive proof that the Shroud was a medieval fraud.

Oddly the original data was unavailable to researchers. But in 2017, a legal request under the Freedom of Information Act obtained the raw information for the first time. Their results, published recently in Archaeometry, show that the issue of the dating of the Turin Shroud is far from settled.

The Turin Shroud is a piece of linen cloth about 14.5 feet long and 3.7 feet wide. On it you can see the brownish outline of a naked bearded man, who sports long hair and is lying with his hands modestly covering his groin. The first solid historical evidence of its existence comes from 1390 when Bishop Pierre d’Arcis wrote to Pope Clement VII stating that the Shroud is a forgery and that its creator had confessed to having created it.

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There are some references to a shroud owned by a French knight earlier in the 14th century and to a burial cloth that was owned by the Byzantine emperors before the sack of Constantinople in 1204, but there’s nothing definitive linking either of these to the Shroud people venerate today. In fact several French churches also claim to own pieces of the shroud of Jesus, but they simply aren’t as famous. From the 14th century onwards, the Shroud’s ownership history is well documented: It was deeded to the House of Savoy in 1453; transferred to Turin in 1578; and has been on display since the 17th century.

Certainly Jesus was buried in a burial cloth of some sort. Three of the New Testament gospel writers mention that Joseph of Arimathea wrapped the body of Jesus in a piece of linen cloth and placed it in his family tomb. The fourth, the Gospel of John, describes Peter finding pieces of burial cloth (one for the head and another for the body) in the empty tomb. There is a reference to (resurrected) Jesus giving the linen cloth to a servant of the Jewish high priest in a second century apocryphal text called the Gospel according to the Hebrews. This shouldn’t be considered historical, however. Dr. Andrew Gregory, author of a commentary on the text, writes that this story was written “to accentuate the [priest’s] wilful unbelief in the resurrection.” In other words, it’s part of an early Christian project against Jewish leadership. Some historians, like John Dominic Crossan, think that the whole story of Jesus’ burial is a fiction. Most who find the burial story credible would state that there was a burial shroud, but we don’t know what happened to it.

In any case, there’s a more than 1350-year gap between the use of a burial shroud and its appearance in the 14th century. Assuming they knew about its survival, it is somewhat strange that early Christians and theologians don’t mention the Shroud. A considerable amount of attention is paid to the ‘discovery’ of the true cross in Jerusalem. Why would ancient historians have passed over this detail? We have to assume that they didn’t know about it. This is something for which it is difficult to account but absence of evidence is not evidence of absence.

Even though it was unlikely to be real, most people thought that the radiocarbon dating would be the silver bullet that would either confirm the inauthenticity of the Shroud or dispel Shroud doubters once and for all. Vatican agreement for testing took decades to obtain and then, finally, in 1987, laboratories in Arizona, Oxford, and Zurich were selected to perform independent tests. On April 21, 1988, a sample was taken from one corner of the cloth and distributed to the three sets of scientists. The resulting publication declared that there was “conclusive evidence” that the linen of the shroud dates to 1260-1390 CE with 95 percent confidence in those results.

Since 2005, however, a growing number of scholars have questioned the results of the now 30-year-old tests. Some claimed, for example, that the area tested was a portion of the cloth that was repaired and that the tested strands reflect those repairs. We know, for example, that efforts were made to restore the Shroud in the 16th century. The fact that testing only used samples from one corner of the cloth makes it impossible to know if this is a claim is correct or not.

Oddly, though, neither academic institutions involved or the British Museum would respond to requests for the original raw data that were held in their archives. (The British Museum also did not respond to a request for comment from The Daily Beast.) It was only when Tristan Casabianca made a request under British law that he received a favourable reply. According to his co-authored article in Archaeometry, the British Museum “made all its files [hundreds of pages worth] ‘not dated or arranged in any order,’ available” to his team.

What Casabianca and co-authors Emanuela Marinelli, Giuseppe Pernagallo, and Benedetto Torrisi discovered is that the results were less conclusive than the Nature article suggests. Casabianca told the Daily Beast that they “examined not only the measurements not included in the Nature article but also the reports and letters from and to the laboratories which mention, for example, foreign material in the samples.” The Shroud might still be medieval, but earlier dates—while statistical outliers—should not be ruled out. Given that technologies of testing have improved in the past 30 years it is possible to make a case for re-testing. Casabianca told me he would like to see an interdisciplinary approach to dating the Shroud employed in any future testing. “Non-destructive tests should be a priority,” he added, suggesting that any future study could carbon date small burned scraps recently removed from the Shroud as part of the restoration process. This hypothetical future testing would need the approval and consent of Pope Francis who, thus far, has hedged his bets on the Shroud. He previously called it an “icon” rather than a relic.

For skeptics, efforts to re-test the Shroud and demonstrate its authenticity are the work of those who have a religious stake in the cloth’s authenticity. Even before his recent article, Casabianca had published a historiographical article on the Shroud’s authenticity and the next event he is hosting on the Turin Shroud will be held at the controversial and decidedly religious Museum of the Bible in January 2020.

What should interest everyone is how hard it was for researchers to obtain copies of the raw data produced during the radiocarbon testing. The British Museum had repeatedly denied requests for the raw data. Bioarchaeologist Dr. Kristina Killgrove, who was not involved in working on the Turin Shroud, told The Daily Beast that “it makes some sense to release info to researchers who want to check it / build on it (and not to release data completely publicly). But to refuse to release data is a big red flag.” Making data available publicly is important Killgrove added, because “replicability is the cornerstone of science, and science can’t progress without the publication of raw data.”

Given everything that is at stake in the Shroud it’s easy to see why scientists would be reluctant to release all of their results (as there are always statistical outliers). It’s also easy to understand why people of faith might be concerned by the strange reluctance of scientists to release their results in full. Perhaps new testing is needed to put the debate to bed once and for all.