Radiocarbon 14 dating of the Shroud of Turin
The Shroud of Turin, a linen cloth commonly associated with the crucifixion and burial of Jesus Christ, has undergone numerous scientific tests, the most notable of which is radiocarbon dating, in an attempt to determine the relic's authenticity. In 1988, scientists at three separate laboratories dated samples from the Shroud to a range of 1260–1390CE, which coincides with the first appearance of the shroud in France in the 1350s.
This dating has been questioned by some, and doubts have been raised in particular regarding the representivity of the sample that was taken for testing.
- 1 History
- 2 Account of the testing process
- 3 Criticisms of the dating result
- 4 Books discussing the carbon-dating
- 5 See also
- 6 References
1978: the creation of S.Tu.R.P.
The idea of scientifically dating the shroud had first been proposed in the 1960s, but permission had been refused because the procedure would have required the destruction of too much fabric (almost 0.05 sq m ≅ 0.538 sq ft). The development in the 1970s of new techniques for radio-carbon dating, which required lower quantities of source material, prompted the Catholic Church to found the Shroud of Turin Research Project (S.Tu.R.P.), which involved about 30 scientists of various religious faiths, including non-Christians.
The S.Tu.R.P. group initially planned to conduct a range of different studies on the cloth, including radio-carbon dating. A commission headed by chemist Robert H. Dinegar and physicist Harry E. Gove consulted numerous laboratories which were able at the time (1982) to carbon-date small fabric samples. The six labs that showed interest in performing the procedure fell into two categories, according to the method they utilised:
- Two used a proportional counter approach:
- Four used accelerator mass spectrometry:
To obtain independent and replicable results, and to avoid conflict between the laboratories, it was decided to let all interested laboratories perform the tests at the same time.
The 1985 rift between S.Tu.R.P. and the candidate labs
In 1982, the S.Tu.R.P. group published the list of tests to be performed on the shroud; these aimed to identify how the image was impressed onto the cloth, to verify the relic's purported origin, and to identify better-suited conservation methods. However, a disagreement between the S.Tu.R.P. group and the candidate laboratories devolved into a P.R. rift: the S.Tu.R.P. group expected to perform the radiometric examination under its own aegis and after the other examinations had been completed, while the laboratories considered radio-carbon dating to be the priority test, which should be completed at the detriment of other tests, if necessary.
The "Turin protocol of 1986"
A meeting with ecclesiastic authorities took place on September 29, 1986 to determine the way forward. In the end, a compromise solution was reached with the so-called "Turin protocol", which stated that:
- carbon-dating would be the only test performed;
- original and control samples, indistinguishable from each other, would be provided (blind test);
- the test would be performed concurrently by seven laboratories, under the joint supervision of the Pontifical Academy of Science, the archbishop of Turin, and the British Museum;
- both dating methods would be adopted;
- the sample offered to each laboratory would weight 28 mg, equivalent to 9 sq. cm. of cloth;
- the British Museum would manage the distribution of the samples;
- laboratories would not communicate with each other during the analysis, nor divulge the results of the tests to anyone but the three supervising authorities.
The protocol was, in fact, violated by the Vatican on at least four counts:
- On April 27, 1987 a Vatican spokesperson announced to the newspaper La Stampa that the procedure would likely be performed by two or three laboratories at most;
- On October 10, cardinal Anastasio Ballestrero officially announced to the seven laboratories that only three of them, namely Oxford, Tucson and Zürich, would be provided with samples taken from the same zone of the Shroud. The British Museum would not provide each laboratory with three samples (one from the Shroud and two control samples);
- The sole supervising institution would end up being the British Museum, headed by Michael Tite;
- The proportional counter method would not be used because this method would require too much Shroud material (gram quantities rather than milligram quantities).
These deviations were heavily criticized. Professor Harry Gove, director of Rochester's laboratory (one of the four not selected by the Vatican), argued in an open letter published in Nature that discarding the blind-test method would expose the results - whatever they may be - to suspicion of unreliability. It remains unclear why the protocol was changed after its public adoption; unofficially, it was suggested that the Church may have wanted to reduce the amount of Shroud material to be removed.
In the heated debate that followed, a Church's spokesperson declared that
(t)he Church must respond to the challenge of those who want it to stop the process, who would want us to show that the Church fears the science.
We are faced with actual blackmail: unless we accept the conditions imposed by the laboratories, they will start a marketing campaign of accusations against the Church, which they will portray as scared of the truth and enemy of science. [...]
The pressure on the ecclesiastic authorities to accept the Turin protocol have almost approached illegality.—Luigi Gonella
The final protocol
The proposed violations to the Turin protocol sparked another acrimonious debate among scientists, so vehement, in fact, that the sampling procedure, scheduled for May 1987, was postponed.
On April 17, 1988, ten years after the S.Tu.R.P. project had been initiated, British Museum scientific director Michael Tite published in Nature the "final" protocol:
- the laboratories at Oxford, Zürich and Tucson would perform the test;
- they would receive one sample weighing 40 mg., sampled from a single portion of weave;
- the laboratories would receive two more samples, clearly distinguishable from the original one—a decision calling on the ethical dependability of the laboratories;
- samples would be delivered to the laboratories' representatives in Turin;
- each test would be filmed;
- there would be no comparison of results (nor communication) between laboratories until the results be certified as definitive, univocal and complete;
- the proportional counter method would not be used because it required gram quantities rather than milligram quantities of shroud material.
Among the most obvious differences between the final version of the protocol and the previous ones stands the decision to sample from a single location on the cloth. This is particularly significant because, should the chosen portion be in any way not representative of the remainder of the shroud, the results would only be applicable to that portion of the cloth.
Account of the testing process
Sampling (April 1988)
Samples were taken on April 21, 1988 in the Cathedral by Franco Testore, an expert on weaves and fabrics, and by Giovanni Riggi, a representative of the maker of bio-equipment "Numana". Testore performed the weighting operations, while Riggi made the actual cut. Also present were Cardinal Ballestrero, four priests, archdiocese spokesperson Luigi Gonella, photographers, a camera operator, Michael Tite of the British Museum and the labs' representatives (who, according the protocol, should in fact not have been present). As a precautionary measure, a piece twice as big as the one required by the protocol was cut from the Shroud; it measured 81 × 21 mm (3.19 × 0.83 in). A strip showing coloured filaments of uncertain origin was discarded. The remaining sample, measuring 81 × 16 mm (3.19 × 0.63 in) and weighing 300 mg, was first divided in two equal parts, one of which was cut into three segments. The unused half was preserved in a sealed container, in case of future need. The labs were also each given three control samples (one more than those originally stated), that were:
- a fragment of weave coming from an Egyptian burial, discovered in 1964 and already carbon-dated to 1100 A.D.;
- a piece of mummy bandage carbon-dated to 200 A.D.;
- a sample of the cloak having belonged to Louis IX of France and preserved in Saint Maximin, Var, France, which had a verifiable provenance and was woven between 1240 and 1270.
In yet another violation of the agreed protocol, the labs did not work separately and simultaneously. Rather, Tucson performed the tests in May, Zürich in June, and Oxford in August, exchanging information in the meantime. On August 26, news of the shroud having been dated to 1350 was leaked to the British newspaper Evening Standard, which published an article on the subject.
On September 28, 1988, British Museum director and coordinator of the study Michael Tite communicated the official results to the Diocese of Turin and to the Holy See. In a well-attended press conference on October 13, Cardinal Ballestrero announced the official results, i.e. that radio-carbon testing dated the shroud to a date of 1260-1390 CE, with 95% confidence. The official and complete report on the experiment was published in Nature. The uncalibrated dates from the individual laboratories, with 1-sigma errors (68% confidence), were as follows:
- Tucson: 646 ± 31 years;
- Oxford: 750 ± 30 years;
- Zürich: 676 ± 24 years old;
- the weighted mean was 689 ± 16 years, which corresponds to calibrated ages of CE 1273-1288 with 68% confidence, and CE 1262-1384 with 95% confidence.
As reported in Nature, Professor Bray of the Instituto di Metrologia 'G. Colonetti', Turin, "confirmed that the results of the three laboratories were mutually compatible, and that, on the evidence submitted, none of the mean results was questionable."
Criticisms of the dating result
The sample was part of a later repair
Although the quality of the radiocarbon testing itself is unquestioned, criticisms have been raised regarding the choice of the sample taken for testing, with suggestions that the sample may represent a medieval repair fragment rather than the image-bearing cloth. It is hypothesised that the sampled area was a medieval repair which was conducted by "invisible reweaving". Since the C14 dating at least four articles have been published in scholarly sources contending that the samples used for the dating test may not have been representative of the whole shroud. These included a 2005 article by Raymond Rogers, who conducted chemical analysis for the Shroud of Turin Research Project and who was involved in work with the Shroud since the STURP project began in 1978. Raymond Rogers argued in a 2005 article that the chemical analysis he performed show traces of tanning products, likely used by medieval weavers to match the colour of the original weave when performing repairs and backing the shroud for additional protection. Rogers stated that after further study he was convinced that: "The worst possible sample for carbon dating was taken." Rogers' conclusions are however based on a study of a few threads that Rogers believed were taken from the C14 shroud sample, but there is no evidence to support their provenance or that they are indeed representative of the C14 sample.
The official report of the dating process, written by the people who performed the sampling, states that the sample "came from a single site on the main body of the shroud away from any patches or charred areas."
In 2008 former STURP member John Jackson rejected the possibility that the C14 sample may have been conducted on a medieval repair fragment, on the basis that the radiographs and transmitted light images taken by STURP in 1978 clearly show that the natural colour bandings present throughout the linen of the shroud propagate in an uninterrupted fashion through the region that would later provide the sample for radiocarbon dating. Jackson stated that this could not have been possible if the sampled area was a later addition. However, Rogers also noted that the presence of vanillin differed markedly between the unprovenanced threads he was looking at, which contained 37% of the original vanillin, while the body of the shroud contained 0% of the original vanillin. He concluded from this that the Shroud is much older than the earlier purported estimates.[unreliable source?] The accuracy of a "vanillin-dating process" has never been tested nor confirmed. Rogers also noted that the thread he examined contained a significant amount of cotton, while such cotton was absent in the main-body of the Shroud.[unreliable source?]
Mechthild Flury-Lemberg is an expert in the restoration of textiles, who headed the restoration and conservation of the Turin Shroud in 2002. She has written that it’s possible to repair a coarsely woven fabric in such a way as to be invisible, if the damage was not too severe and the original warp threads are still present, but that it is never possible to repair a fine fabric in a way which would be truly invisible, as the repair will always be "unequivocally visible on the reverse of the fabric." She criticized the theory that the C14 tests were done on an invisible patch as "wishful thinking". She states that Gabriel Vial, a textile expert who was present when the sample was taken, confirmed repeatedly that the sample was taken from the original cloth, and that "neither on the front nor on the back of the whole cloth is the slightest hint of a mending operation, a patch or some kind of reinforcing darning, to be found."
In 2010, professors of statistics Marco Riani and Anthony C. Atkinson wrote in a scientific paper that the statistical analysis of the raw dates obtained from the three laboratories for the radiocarbon test suggests the presence of contamination in some of the samples. They conclude that: "The effect is not large over the sampled region … our estimate of the change is about two centuries."
In December 2010 Professor Timothy Jull, a member of the original 1988 radiocarbon-dating team and editor of the peer-reviewed journal Radiocarbon, coauthored an article with a textile expert in that journal. They examined a portion of the radiocarbon sample left over from the section used by the University of Arizona in 1988 for the carbon dating exercise, and found no evidence of a repair, nor of any dyes or other treatments. They concluded that the radiocarbon dating had been performed on a sample of the original shroud material.
Professor Christopher Ramsey of the Oxford Radiocarbon Accelerator Unit who observed in 2011 that "There are various hypotheses as to why the dates might not be correct, but none of them stack up." However, in late March 2013 Giulio Fanti, professor of mechanical and thermal measurement at the University of Padua conducted a battery of experiments on various threads that he believes were cut from the shroud during the 1988 Carbon-14 dating, and concluded that they dated from 300 B.C. to 400 A.D., potentially placing the Shroud within the lifetime of Jesus of Nazareth. Cesare Nosiglia, Archbishop of Turin and Custodian of the Holy Shroud, responded that "as it is not possible to be certain that the analyzed material was taken from the fabric of the Shroud, the Holy See and the Papal Custodian declare that no serious value can be recognized to the results of such experiments."
The dating contradicts other evidence
Scholar Raymond Rogers, who was a director of the Shroud of Turin Research Project, argued in the scientific journal Thermochimica Acta that: "The fact that vanillin cannot be detected in the lignin on shroud fibers, Dead Sea scrolls linen, and other very old linens indicate that the shroud is quite old. A determination of the kinetics of vanillin loss suggest the shroud is between 1300- and 3000-years old. Even allowing for errors in the measurements and assumptions about storage conditions, the cloth is unlikely to be as young as 840 years".
It has however been stated that Roger’s vanillin-dating process is untested, and the validity thereof is suspect. The deterioration of vanillin is heavily influenced by the temperature of its environment - heat strips away vanillin rapidly – and the shroud has been subjected to temperatures high enough to melt silver and scorch the cloth. Rogers’ analysis is also questioned by skeptics such as Joe Nickell, himself a non-scientist, who reasons that the conclusions of the author, Raymond Rogers, result from "starting with the desired conclusion and working backward to the evidence".
The sample was contaminated
In 1993 Dr. Leoncio A. Garza-Valdes discovered the presence of polyhydroxyalkanoate (mcl-PHA)-producing bacteria Leobacillus rubrus on Shroud's fabric and confirmed their presence on three Egyptian mummies. According to Garza-Valdes, "the scientists that carried out the radiocarbon dating of the Shroud of Turin in 1988, were not aware of the presence of this unsuspected contaminant (natural plastic coating)". Garza-Valdes outlines further, that while studying thin sections from the Shroud fibers it was found that "more than 60% of the fibers' area is bioplastic". Pictorial evidence dating from c. 1690 and 1842 indicates that the corner used for the dating and several similar evenly spaced areas along one edge of the cloth were handled each time the cloth was displayed, the traditional method being for it to be held suspended by a row of five bishops. Wilson and others contend that repeated handling of this kind greatly increased the likelihood of contamination by bacteria and bacterial residue compared to the newly discovered archaeological specimens for which carbon-14 dating was developed. Bacteria and associated residue (bacteria by-products and dead bacteria) carry additional carbon-14 that would skew the radiocarbon date toward the present.
Professor Harry Gove, director of Rochester's laboratory (one of the laboratories not selected to conduct the testing), has also hypothesised that a “bioplastic” bacterial contamination, which was unknown during the 1988 testing, would render the tests inaccurate. He has however also acknowledged that the samples had been carefully cleaned with strong chemicals before testing.
STURP scientist Dr John Jackson has discounted the hypothesis that the sample was contaminated by more recent bioplastic residues from microbial action, on the basis that the samples were carefully cleaned first to eliminate this kind of contamination, and that the quantity of microbial mass required to skew the results would be significantly greater than the mass of the linen itself.
Rodger Sparks, a radiocarbon expert from New Zealand, had countered that an error of thirteen centuries stemming from bacterial contamination in the Middle Ages would have required a layer approximately doubling the sample weight. Because such material could be easily detected, fibers from the shroud were examined at the National Science Foundation Mass Spectrometry Center of Excellence at the University of Nebraska. Pyrolysis-mass-spectrometry examination failed to detect any form of bioplastic polymer on fibers from either non-image or image areas of the shroud. Additionally, laser-microprobe Raman analysis at Instruments SA, Inc. in Metuchen, New Jersey, also failed to detect any bioplastic polymer on shroud fibers.
Others have suggested that the silver of the molten reliquiary and the water used to douse the flames may have catalysed the airborne carbon into the cloth. The Russian Dmitri Kouznetsov, an archaeological biologist and chemist, claimed in 1994 to have managed to experimentally reproduce this purported enrichment of the cloth in ancient weaves, and published numerous articles on the subject between 1994 and 1996. Kouznetsov's results could not be replicated, and no actual experiments has been able to validate this theory, so far. Professor Gian Marco Rinaldi and others proved that Kouznetsov never performed the experiments described in his papers, citing non-existent fonts and sources, including the museums from which he claimed to have obtained the samples of ancient weaves on which he performed the experiments. The Russian was arrested in 1997 on American soil under allegations of accepting bribes by magazine editors to produce manufactured evidence and false reports.
Likewise proposed was a reaction with carbon monoxide (CO), a trace gas present in air, which it was claimed could add additional “fresh” C14 to the sample. However carbon monoxide does not undergo significant reactions with linen which could result in an incorporation of a significant number of CO molecules into the cellulose structure.
The 2008 documentary Sindone, prove a confronto (lit., "The Shroud, comparing evidence") by David Rolfe suggested that the quantity of carbon 14 found on the weave may have been significantly affected by the weather, the conservation methods employed throughout the centuries, as well as the volatile carbon generated by the fire that damaged the shroud while in Savoy custody at Chambéry. Other theories include that candle smoke (rich in carbon dioxide) and the volatile carbon molecules produced during the two fires may have altered the carbon content of the cloth, rendering carbon-dating unreliable as a dating tool.
The calculations were done incorrectly
In 1994, J. A. Christen applied a strong statistical test to the radiocarbon data and concludes that the given age for the shroud is, from a statistical point of view, correct.
However critics claim to have identified statistical errors in the conclusions published in Nature: including: the actual standard deviation for the Tucson study was 17 years, not 31, as published; the chi-square distribution value is 8.6 rather than 6.4, and the relative significance level (which measures the reliability of the results) is close to 1% - rather than the published 5%, which is the minimum acceptable threshold. None of these errors would however produce an altered dating supportive of a 1st Century manufacture.
In 2008 the director of the Oxford Radiocarbon Accelerator Unit, Christopher Ramsey, told the BBC that "With the radiocarbon measurements and with all of the other evidence which we have about the Shroud, there does seem to be a conflict in the interpretation of the different evidence". Ramsey has stressed that he would be surprised if the 1988 tests were shown to be far off, let alone "a thousand years wrong", but said that he would keep an open mind.
Books discussing the carbon-dating
There are two books with detailed treatment of the Shroud's carbon dating, including not only the scientific issues but also the events, personalities and struggles leading up to the sample taking. The books offer opposite views on how the dating should have been conducted, and both are critical of the methodology finally employed.
In Relic, Icon or Hoax? Carbon Dating the Turin Shroud (1996; ISBN 0-7503-0398-0), Harry Gove provides an account of the interaction between Prof Carlos Chagas, chairman of the Pontifical Academy of Sciences, and Cardinal Ballestrero, with Gove and Gonella. He provides a detailed record of meetings, telephone conversations and correspondence.
The Rape of the Turin Shroud by William Meacham (2005; ISBN 1-4116-5769-1) devotes 100 pages to the carbon dating. Meacham is also highly critical of STURP and Gonella, and also of Gove. He describes the planning process from a very different perspective (both he and Gove were invited along with 20 other scholars to a conference in Turin in 1986 to plan the C-14 protocol) and focuses on what he claims was the major flaw in the dating: taking only one sample from the corner of the cloth. Meacham reviews the main scenarios that have been proposed for a possibly incorrect dating, and claims that the result is a "rogue date" because of the sample location and anomalies. He points out that this situation could easily be resolved if the Church authorities would simply allow another sample to be dated, with appropriate laboratory testing for possible embedded contaminants.
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- Nell'occasione si era aggiunto ai candidati anche il laboratorio francese di Gif-sur-Yvette.
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- The Turin Shroud is fake. Get over it Tom Chivers in the Daily Telegraph 20 Dec 2011
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