Radiocarbon Dating Of The Shroud Of Turin

The Shroud of Turin, a linen cloth that tradition associates with the crucifixion and burial of Jesus, 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 1260–1390 CE, which coincides with the first certain appearance of the shroud in the 1350s and is much later than the burial of Jesus in 30 or 33 CE. Aspects of the 1988 test continue to be debated. Some technical concerns have been raised about radiocarbon dating of the Shroud, with active papers being published through 2019. In 2019, an editor of ''Nature'' (the journal in which the radiocarbon dating study was published) stated that "Nothing published so far on the shroud ... offers compelling reason to think that the 1989 study was substantially wrong – but apparently it was not definitive either".

Background

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 at the time would have required the destruction of too much fabric (almost 0.05 sq m ≅ 0.5 sq ft). The development in the 1970s of new techniques for radio-carbon dating, which required much smaller quantities of source material, prompted the Roman 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:
** Brookhaven National Laboratory, Upton, New York, United States;
** Atomic Energy Research Establishment, Harwell, Oxfordshire, England;
* Four used accelerator mass spectrometry:
** Nuclear Structure Research Laboratory, University of Rochester, Rochester, New York, United States;
** the University of Oxford, England;
** University of Arizona, Tucson, Arizona, United States;
** ETH Zürich, Switzerland.
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.

Disagreements between S.Tu.R.P. and candidate laboratories

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 turned into a public relations 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 prime test, which should be completed at the detriment of other tests, if necessary.

The 1986 Turin protocol

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 weigh 28 mg, in total equivalent to 9 cm² of cloth;Mechtilde Flury-Lemberg, esperta mondiale in tessuti appartenente alla Fondazione Abegg di Berna. In altre occasioni verrà chiamata per eseguire studi sul lenzuolo; in particolare nel 2000 fece parte di una commissione creata per studiare i metodi migliori per la conservazione del lino; nel 2002 ha eseguito alcuni studi sulle toppe che coprivano i buchi causati dall'incendio di Chambery.
* 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 Vatican subsequently decided to adopt a different protocol instead.
* On April 27, 1987, a Vatican spokesperson announced to the newspaper ''La Stampa'' that the procedure would probably be performed by two or three laboratories at most;
* On October 10, Cardinal Anastasio Ballestrero officially announced to the seven laboratories that the proportional counter method would not be used because this method would require too much Shroud material (gram quantities rather than milligram quantities). Only three laboratories, namely Oxford, Tucson, and Zürich, would be provided with Shroud samples to be tested.
* The sole supervising institution would be the British Museum, headed by Michael Tite.
These deviations were heavily criticized.

The blind-test method was abandoned, because the distinctive three-to-one herringbone twill weave of the shroud could not be matched in the controls, and it was therefore still possible for a laboratory to identify the shroud sample. Shredding the samples would not solve the problem, while making it much more difficult and wasteful to clean the samples properly."Radiocarbon Dating of the Shroud of Turin", Damon et al, ''Nature'', Vol. 337, No. 6208, pp. 611–15, 16th February, 1989, 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. However, in a 1990 paper Gove conceded that the "arguments often raised, … that radiocarbon measurements on the shroud should be performed blind seem to the author to be lacking in merit; … lack of blindness in the measurements is a rather insubstantial reason for disbelieving the result."

In the heated debate that followed, Church spokesperson Luigi Gonella declared that

The final protocol

The proposed changes to the Turin protocol sparked another heated debate among scientists, and the sampling procedure 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 each receive one sample weighing 40 mg, sampled from a single portion of weave;
* the laboratories would each receive two control samples, clearly distinguishable from the shroud sample;
* 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 the 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 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.

A further, relevant difference was the deletion of the blind test, considered by some scholars as the very foundation of the scientific method. The blind-test method was abandoned because the distinctive three-to-one herringbone twill weave of the shroud could not be matched in the controls, and a laboratory could thus identify the shroud sample. Shredding the samples would not solve the problem, while making it much more difficult and wasteful to clean the samples properly.

Testing process

Sampling

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.

As a precautionary measure, a piece twice as big as the one required by the protocol was cut from the Shroud; it measured . An outer strip showing coloured filaments of uncertain origin was discarded. The remaining sample, measuring and weighing 300 mg, was first divided in two equal parts, one of which was preserved in a sealed container, in the custody of the Vatican, in case of future need. The other half was cut into three segments, and packaged for the labs in a separate room by Tite and the archbishop. The lab representatives were not present at this packaging process, in accordance with the protocol.

The labs were also each given three control samples (one more than originally intended), that were:
* a fragment of weave coming from an Egyptian burial, discovered in 1964 and already carbon-dated to 1100 CD;
* a piece of mummy bandage carbon-dated to 200 CE;
* 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.

Completion of tests

Tucson performed the tests in May, Zürich in June, and Oxford in August, and communicated their results to the British Museum.

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.

Official announcement

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 standard deviation errors (68% confidence), were as follows:
* Tucson: 646 ± 31 years;
* Oxford: 750 ± 30 years;
* Zürich: 676 ± 24 years old;
* the unweighted mean was "691 ± 31 years", which corresponds to calibrated ages of "1273–1288 CE" with 68% confidence, and "1262–1312, 1353–1384 CE cal" with 95% confidence.
As reported in ''Nature'', Anthos 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 test results

Medieval repairs

Although the quality of the radiocarbon testing itself is not questioned by experts, 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 an article by American chemist Raymond Rogers, Director of Chemical Research for the Shroud of Turin Research Project (STURP), who was involved in work with the Shroud since the STURP project began in 1978. Rogers took 32 documented adhesive-tape samples from all areas of the shroud and associated textiles during the STURP process in 1978. He received 14 yarn segments from Luigi Gonella (from the Department of Physics at the Polytechnic University of Turin) on 14 October 1979, which Gonella told him were from a sample removed by Gilbert Raes of the Ghent Institute of Textile Technology in 1973. On 12 December 2003, Rogers received samples of both warp and weft threads that Luigi Gonella claimed to have taken from the radiocarbon sample before it was distributed for dating. The actual provenance of these threads is uncertain, as Gonella was not authorized to take or retain genuine shroud material, but Gonella told Rogers that he excised the threads from the center of the radiocarbon sample.

Raymond Rogers stated in a 2005 article that he performed chemical analyses on these undocumented threads, and compared them to the undocumented Raes threads as well as the samples he had kept from his STURP work. He stated that his analysis showed: "The radiocarbon sample contains both a gum/dye/mordant coating and cotton fibers. The main part of the shroud does not contain these materials." He speculated that these products may have been used by medieval weavers to match the colour of the original weave when performing repairs and backing the shroud for additional protection. Based on this comparison Rogers concluded that the undocumented threads received from Gonella did not match the main body of the shroud, and that in his opinion: "The worst possible sample for carbon dating was taken."

As part of the testing process in 1988, Derbyshire laboratory in the UK assisted the Oxford University radiocarbon acceleration unit by identifying foreign material removed from the samples before they were processed.Radiocarbon