Carbon 14 Dating the Shroud of Turin: Now We Know
Carbon 14 Dating for Students and Everyone
One might think the Papal custodians of the Shroud of Turin would be pleased. The primary skeptical argument, carbon 14 dating, had been removed from serious consideration. But they were not happy.
Mention of the Shroud of Turin in the media has become quite commonplace. But as often as not, old information or incorrect information is mentioned. Because the shroud is a religious object, believed by many to be the burial cloth of Jesus, and because scientists and historians have yet to prove or disprove its authenticity, it is controversial and interesting.
And nothing has been more controversial than the carbon 14 dating of the Shroud.
Until recently, skeptics had the upper hand in the ongoing debate about its authenticity. Carbon 14 dating in 1988 seemed to show that it was medieval. Researchers, who were not experts in radiocarbon dating, but nonetheless convinced the shroud was authentic, tried to explain why the scientific dating was incorrect. Often cited in the news media in an attempt at balanced reporting, these explanations – one was that a fire in 1532 changed the age of the cloth, another was that a bioplastic-polymer growing on the cloth contaminated the sample – lacked scientific credibility. Scientists, who were experts in radiocarbon dating, pooh-poohed these explanations.
|Photomicrograph of fibers from warp segment of carbon 14 sample. It is chemically unlike the rest of the shroud. That is a problem.|
It was not until 2005 that things changed. An article appeared in a peer-reviewed scientific journal Thermochimica Acta, which proved that the carbon 14 dating was flawed because the sample was invalid. Moreover, this article, by Raymond N. Rogers, a well-published chemist, and a Fellow of the Los Alamos National Laboratory, explained why the cloth was much older. It was at least twice as old as the radiocarbon date, and possibly 2000 years old.
Peer-reviewed scientific journals are important. It is the way scientists normally report scientific findings and theories. Articles submitted to such journals are carefully reviewed for adherence to scientific methods and the absence of speculation and polemics. Reviews are often anonymous. Facts are checked and formulas are examined. The review procedure sometimes takes months to complete, as it did for Rogers.
It was Nature, another prestigious peer-reviewed journal, that in 1989, reported that carbon 14 dating ‘proved’ the shroud was a hoax. Rogers found no fault with the article in Nature. Nor did he find fault with the quality of the carbon 14 dating. He defended it. What Rogers found was that the carbon 14 sample was taken from a mended area of the cloth that contained significant amounts of newer material. This was not the fault of the radiocarbon laboratories. But it did show that the dating was invalid.
Immediately after the publication of Rogers’ paper, Nature published a commentary by scientist-journalist Philip Ball. “Attempts to date the Turin Shroud are a great game,” he wrote, “but don't imagine that they will convince anyone . . . The scientific study of the Turin shroud is like a microcosm of the scientific search for God: it does more to inflame any debate than settle it.” Later in his commentary Ball added, “And yet, the shroud is a remarkable artefact, one of the few religious relics to have a justifiably mythical status. It is simply not known how the ghostly image of a serene, bearded man was made.”
Ball, who understood the chemistry of the shroud’s images, rejected a notion popularized by many news accounts that Leonardo da Vinci created the image using primitive photography. He called the idea flaky. He also debunked the sometimes reported speculation that the image was “burned into the cloth by some kind of release of nuclear energy” from Jesus’ body. This he said was wild.
Almost all serious shroud researchers agree with Ball on these points. When flaky and wild ideas appear in newspaper articles or on television, as they often do, scientists cringe. Rogers referred to those who held such views as being part of the “lunatic fringe” of shroud research. But Rogers was just as critical of those who, without the benefit of solid science, declared the shroud a fake. They, too, were part of the lunatic fringe.
|Yellow dye can be seen from spliced thread. Newer material was dyed with alizarin from madder root to match age-yellowed older thread.|
The idea that the shroud had been mended in the area from which the carbon 14 samples had been taken had been floating around for some time. But no one paid much attention. In 1998, Turin’s scientific adviser, Piero Savarino, suggested, “extraneous substances found on the samples and the presence of extraneous thread (left over from ‘invisible mending’ routinely carried on in the past on parts of the cloth in poor repair)” might have accounted for an error in the carbon 14 dating. Longtime shroud researchers Sue Benford and Joe Marino independently developed the same idea and explored it with several textile experts and Ronald Hatfield of the radiocarbon dating firm Beta Analytic. The art of invisible reweaving, Benford and Marino discovered, was commonly used in the Middle Ages to repair tapestries. Why not the shroud, they thought? The believed they saw evidence of it.
But the skeptically minded Rogers did not agree. He had already debunked every other argument so far offered to explain why the carbon 14 dating might be wrong. According to Ball, “Rogers thought that he would be able to ‘disprove [the] theory in five minutes’.” Instead he found clear evidence of discreet mending. He also showed, with chemistry, that the shroud was at least thirteen hundred years old. And he proved, beyond any doubt, that the sample used in 1988 was chemically unlike the rest of the shroud. The samples were invalid. The 1988 tests were thus meaningless.
In words that seem strange in a scientific journal that once had bragging rights to claim that the shroud was not authentic, Ball wrote: “And of course 'authenticity' is not really a scientific issue at all here: even if there were compelling evidence that the shroud was made in first-century Palestine, that would not even come close to establishing that the cloth bears the imprint of Christ.”
One might think the Papal custodians of the Shroud of Turin would be pleased. The head of the skeptical argument, the carbon 14 dating, had been severed. The shroud might be 2000 years old, after all. But like Hydra, the Greek mythological beast, controversy grew a weird new head. The 1988 carbon 14 dating was off the table. And Ball, who was familiar with the evidence, had confirmed what all shroud researchers had been saying for years: the images were not painted. Moreover, a 2003 article in the peer-reviewed scientific journal Melanoidins by Rogers and Anna Arnoldi, a chemistry professor at the University of Milan, demonstrated that the images were in fact a chemical caramel-like darkening of an otherwise clear starch and polysaccharide coating on some of the shroud’s fibers. They suggested a natural phenomenon might be the cause. If this could be proven, the images could be explained in non-miraculous, scientific terms.
|Photomicrograph of fibers from the center of the radiocarbon sample in water. Gum material is swelling and detaching from fibers. Chemical tests show that dye is yellow alizarin from madder root complexed with alum, a common mordant. Several cotton fibers are also visible. Cotton, alizarin and gum are only found in the C14 sample area of the shroud.|
The Papal Custodians of the Shroud in Turin were not pleased. They had been responsible for selecting the sample from a corner of the cloth. They had ignored scientific protocols to which they had previously agreed. These protocols called for multiple samples from multiple locations. And in 2002, during a restoration of the shroud, they had examined the area from which the samples were cut and had not found any visual evidence of mending.
But then no one else had noticed it, either. It took microscopy to see spliced threads where newer fibers were dyed to match age-yellowed fibers. It took microchemical analysis to find alizarin dye from madder root, alum and plant gum. This was the dyestuff used in medieval times.
Researchers and thousands of people who follow shroud research were dismayed when, within days of Rogers’ paper, Turin’s Monsignor Giuseppe Ghiberti told an Italian newspaper, “I am astonished that an expert like Rogers could fall into so many inaccuracies in his article. I can only hope, indeed, also think that the C14 dating is rectifiable (the method, in fact, has its own uncertainties), but not on the basis of the 'darn' theory.”
The restoration, itself, was very controversial. Turin officials had done the work in secret. They had scraped the shroud, vacuumed it, wet it with fine mist, and stretched it with weights to remove wrinkles. Forensic material, best studied in situ, such as pollen and dirt, was removed and placed in bottles. Researchers wondered how much blood was scraped away. And they wondered how much the fragile images were damaged or loosened by the stretching and scraping since they are part of a fragile coating that is very thin and easily removed. Many, if not most shroud researchers felt the restoration was scientifically and preservation-wise reckless. The newer evidence in scientific journals was drawing attention to how Turin was caring for the cloth and how they were treating scientific evidence.
Significant Supporting Data on the Carbon 14 Dating the Shroud of Turin
1) John L. Brown, formerly Principal Research Scientist at the Georgia Tech Research Institute's Energy and Materials Sciences Laboratory at the Georgia Institute of Technology, independently confirmed many of Rogers’ findings.
2) In early 2004, the Journal of Research of the National Institute of Standards and Technology published an important paper by Lloyd A. Currie. Currie, a highly regarded specialist in the field of carbon 14 dating and an NIST Fellow Emeritus, cited Rogers and Arnoldi (from another paper) and gave their work credence. Currie’s NIST paper also set aside any argument that radiocarbon labs had done anything wrong in dating the Shroud of Turin. It debunked the heat-effect, contamination and bioplastic polymer hypotheses. Significantly, it recognized that discreet mending, soon to be demonstrated by Rogers in his peer-reviewed article, was a viable explanation. And it raised the issue of poor sampling by Turin. According to Currie, the original sampling protocol requiring multiple samples from different locations on the cloth was clearly violated by the Papal Custodians of the Shroud. Had the protocol been followed the discreet mending would have been noticed in 1988.
3) Several textile experts, at the behest of Sue Benford and Joseph Marino, examined documenting photographs of the samples and found visual evidence of reweaving. Based on estimates from these photographs, and an a historically-likely suggested date for reweaving, Ronald Hatfield of the radiocarbon dating firm Beta Analytic estimated that the cloth might be 2000 years old.
4) In 1997, Remi Van Haelst, a Belgium chemist, conducted a series of statistical analyses that strongly challenged the veracity of the conclusions of the C14 dating. Significantly, he found serious disparities in measurements between the three laboratories and between the sub-samples (various tests and observations performed by the labs). Bryan Walsh, a statistician, examined Van Haelst’s work and further studied the measurements. The essential conclusions were that the samples, and indeed the divided samples used in multiple tests, contained different levels of the C14 isotope. The differences were sufficient to conclude that the sample were non-homogeneous and thus of questionable validity. Walsh found a significant relationship between various sub-samples and their distance from the edge of the cloth.
5) Ultraviolet and x-ray photographs, taken in 1978 before the carbon 14 dating samples were taken, show that there are chemical differences between the sample area and surrounding areas of the cloth.
6) In 1988, Edward Hall, then the director of Oxford University's Radiocarbon Laboratory, had seen cotton fibers that might be from mending. That same year, in Textile Horizons in an article entitled "Rogue Fibers Found in Shroud," P. H. Smith suggested that those cotton fibers were suspicious and might have been part of repairs.
Moreover, Rogers found: When the linen wrapping from the Dead Sea Scroll were tested for vanillin, none was found. Vanillin (vanilla) is produced by the thermal decomposition of lignin, a complex polymer non-carbohydrate constituent of plant material including flax. Found in medieval linen but not in much older material, it diminishes and disappears with time. There is no vanillin in the flax fibers of the shroud except in the corner from which the carbon 14 samples were taken. While this is not an accurate method for determining the age of linen because it depends on the average storage temperature over many centuries, it is useful as a gauge or sniff test for checking carbon 14 dating. Assuming that the shroud has been stored at an average temperature 77° Fahrenheit, which is quite warm given that for at least the last seven hundred years it had been stored in northern European cathedrals, it is at least 1300 years old. It could be older but there is no way to know that. On the other hand, linen manufactured in 1260, the oldest date for the shroud determined by carbon 14 testing, should have retained about 37% of its vanillin. Not only does this verify that the carbon 14 sample is chemically different from the rest of shroud, it proves that the carbon 14 sample contains much newer material.
© 2004 Daniel R. Porter, Bronxville, New York