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.Jumper, E.J. – An Overview of the Testing Performed by the Shroud of Turin Research Project with a Summary of Results – IEEE 1982 Proceedings of the International Conference on Cybernetics and Society, October 1982, pp. 535–37. 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.Robert Patruno. "E quel falso lenzuolo diventò un business". La Repubblica, October 15, 1988, p. 20.

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:Schafersman, S. D. "Are the STURP scientists pseudoscientists?" The Microscope 30 No. 3, 1982, pp. 232–34. 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.Power, B.A. "Implications of Energy Compressibility for Shroud of Turin Image-Process and Carbon-14 Dating" – Typescript – Dorval, Quebec, Canada, Jan. 20, 1984, pp. 1–11.

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",Jennings, P. – Art Historian Not Convinced the Shroud is a Fake – Our Sunday Visitor, Oct. 23, 1988, p. 24.Jennings, P. "Shroud of Turin to Undergo Radiocarbon Testing" Our Sunday Visitor, Feb. 14, 1988, p. 3. 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 sevenNell'occasione si era aggiunto ai candidati anche il laboratorio francese di Gif-sur-Yvette. 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;Terrasi, F. "Lettera – Sulla datazione del carbonio-14" Didattica delle Scienze, No. 149, Ottobre 1990, pp. 59–60.van Haelst, R. "Radiocarbon dating and the Shroud of Turin" Typescript, Symposium Scientifique International de Paris sur le Linceul de Turin, 7–8 Septembre 1989, pp. 1–29. 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.Prestipino, C.A. "Il carbonio-14 e la S. Sindone" Didattica delle Scienze, No. 147, Aprile 1990, pp. 16–28.Prestipino, C.A. "Replica – Sulla datazione del carbonio-14" Didattica delle Scienze, No. 149, Ottobre 1990, pp. 60–62.

The Vatican subsequently decided to adopt a different protocol instead.Anderson, I. "Vatican undermines tests on Turin shroud" New Scientist, January 21, 1988, p. 22. 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).White, N.R., D. Phil Thesis, Oxford, 1981Van Oosterwyck-Gastuche, M.-C. "Age medieval du Linceul de Turin: Les étapes d'un bluff technologique" Science et Foi- Les Nouvelles du CESHE (Cercle Scientifique et Historique, Tournai, Belgique), No. 19, 1eme trimestre 1991, pp. 11–29. 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.Raloff, J. "Controversy Builds as Shroud Tests Near" Science News, April 16, 1988, p. 245.

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.Anonymous "Shroud Dating Isn't Ironed Out" Science News, 1987, 132, p. 302.

On April 17, 1988, ten years after the STURP 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.Marino, J.G., and Benford, M.S. (2000). "Evidence for the Skewing of the C-14 Dating of the Shroud of Turin Due to Repairs". 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.Marino, J. "The Shroud of Turin and the Carbon 14 Controversy" Fidelity, Feb. 1989, pp. 36–45.

A further, relevant difference was the deletion of the blind test, considered by some scholars as the very foundation of the scientific method.Van Oosterwyck-Gastuche, M.-C. "Le Sain Suaire et le radiocarbone" Sel de la Terre, No. 20, Printemps 1997, pp. 31–54.Van Oosterwyck-Gastuche, M.-C. "Que penser des ages radiocarbone?" Science et Foi- Les Nouvelles du CESHE (Cercle Scientifique et Historique, Tournai, Belgique), No. 30, 4eme trimestre 1993, pp. 23–31.Whanger, A.D., Whanger, M. "Comments on the C-14 Carbon Dating Results on the Shroud of Turin"Typescript, Sept. 29, 1988, pp. 1–4. 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 Crucifixion of Jesus, Completely Revised and Expanded: A Forensic Inquiry