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 AD, 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 AD. Aspects of the 1988 test continue to be debated. Despite some technical concerns that have been raised about radiocarbon dating of the Shroud, no radiocarbon-dating expert has asserted that the dating is substantially unreliable. 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 the Shroud of Turin Research Project 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 (STURP), which involved about 30 scientists of various religious faiths, including non-Christians. The STURP 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 STURP and candidate laboratories In 1982, the STURP 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 STURP group and the candidate laboratories turned into a public relations rift: the STURP 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; 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. 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 [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.
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