Radiocarbon 14 dating of the Turin Shroud

Radiocarbon dating of the Turin Shroud was the most famous scientific study performed on the artifact. The radiocarbon dating was carried out in 1988 and dated the cloth is to between 1260 and 1390 C.E., compatible with the first recorded mention of the relic's existence in 1353.

This dating is generally accepted by most of the scientific community and by those who believe the Shroud to be inauthentic. Shortly after the study, the conclusions were accepted by a part of the Catholic Church too, according to the Turin archbishop Anastasio Ballestrero. Criticisms have been raised about the reliability of the study, primarily by supporters of the Shroud's authenticity.

History

1978: the establishment of STURP

New experimental techniques for radiocarbon dating, which required lower quantities of source material prompted the Catholic Church to establish the Shroud of Turin Research Project (STURP), a group composed of almost 30 scientists of various religious faiths, including atheists.

The idea of scientifically dating the Shroud had been proposed in the 1960s, but permission was refused as it would have required removing too much fabric (almost 500 cm²).

From its inception, STURP put forward plans for performing different studies on the cloth, including radiocarbon dating. For this reason, in 1982 a commission headed by the chemists Robert H. Dinegar and Harry E. Gove consulted various laboratories skilled on dating small fabric samples. Six laboratories showed interest in performing this dating. These ones used two different methods:
*two using the proportional counter:
**Brookhaven National Laboratory, Upton, New York, USA;
**Atomic Energy Research Establishment, Harwell, Oxfordshire, UK;
*four using mass spectrometry:
**the Rochester laboratory, New York, USA;
**the University of Oxford, UK;
**Tucson University, Arizona, USA;
** ETH Zurich, Switzerland.

1985: the break between STURP and laboratories

In 1984 STURP published the list of studies to be performed on the Shroud: these studies aimed to explain how the image was woven onto the cloth, to verify the reliability and to find better conservation methods.

The last goal implied radiocarbon dating, so six pieces of fabric were were collected from the Shroud. The great marketing opportunity from the importance of the exam brought the laboratories into competition for the contract.

A split between STURP and the laboratories occurred: the former intended to perform the radiometric exam under its own aegis and only after the other exams, while the laboratories considered the radiocarbon dating to be of maximum importance to the exclusion of other tests. Thus, during a conference on radiocarbon dating in Trondheim in 1985, the laboratories' representatives announced the end of collaboration with STURP, presenting a new program divided into seven parts:
*the British Museum will co-direct analysis;
*STURP will be involved only for the sampling;
*the British Museum will receive the samples, knowing but not revealing their dating;
*the samples must be provided in such a way as to be indiscernible from the original;
*the laboratories must not reveal the dating to anyone but the co-director of the British Museum, Michael Tite;
*the laboratories will be free to perform the exams through the techniques they choose;
*the results, before being published, will be communicated to the Vatican.

The protocol was approved by Carlos Chagas Filho, neurologist and president of the Pontifical Academy of Sciences.

1986: the "Turin protocol"

As the acceptance from the Vatican of the mutiny of Trondheim erase the role of STURP, it was stated to organise a new meeting in order to solve the diatribe.On 29 September 1986 was hold in Turin a conference organised by the ecclesiastic authorities to approve the original STURP protocol or the laboratories' one. The last one was accepted and was stated to perform the radiocarbon dating exam only.So it was wrote the so called "Turin protocol", which included these decisions:
*the dating will be performed by seven laboratories, under the control of the "Accademia pontificia delle Scienze", the Turin archbishop and the British Museum;
*both dating methods will be adopted;
*the sample offered to each laboratory will weight 28 mg, that is 9 cm². The British Museum will manage the distribution of the samples.
*the laboratories will not be allowed to keep in communication during the analysis and will be allowed to communicate the results only to the three controlling organisms;
*as the dating has the greatest priority, the other exams are moved.The British Museum gave to each laboratory three sample (the original one and two others indiscernible but not belonging to the Shroud), following an operating method usually adopted in these cases, called blind test.Anyway, despite the accords, at least three of these five point are going to be violated, by Vatican's decisions. On April 27th 1987 in fact Gonella announced to La Stampa (an Italian leading newspaper) that the dating would have been performed by two or three laboratories. On October 10th the cardinal Anastasio Ballestrero declared officially to the seven laboratories that the exam would have been committed only to three of them, that are Oxford, Tucson and Zurich, and using therefore only three samples, taken by the same cloth zone. The unique institution controlling the exams would have been the British Museum, headed by Michael Tite.This choice made from Vatican was heavily criticized: for instance, professor Harry Gove, Rochester laboratory's rector, one of the four discarded, argue in a letter pubblished on the magazine Nature that the sampling in a unique portion of the Shroud would have caused the risk of contaminations and that the result obtained in this way would have been less reliable than that one performed following the Turin protocol.The motivations which motivated the Catholic Church to adopt these decisions are nowadays still ignored: the unofficial motivation was that reducing the number of laboratories, it would have been sampled less weave from the Shroud.Anyway it was not saved so much weave as expected: in fact for the dating operations will be sampled 300 mg from the Shroud instead of 200 mg. Afterwards Gonella said:Gonella will define "mafious" the executors of the experiments.In the three chosen laboratories was not also used the proportional counter method, considered as the most reliable for little samples' dating. This caused the protest of some scientists, among which Paul Maloney, president of ASSIST ("Association of Scientists and Scholars International of the Shroud of Turin").

The definitive protocol

The changes to the Turin protocol caused other polemics among scientists involved in the operation and the sampling, stated in May 1987, was postponed.On April 17th 1988. in a letter published by Nature, Michael Tite summarized so the definitive protocol:
*the three chosen laboratories are Oxford, Zurich and Tucson;
*these three will receive a sample each one weighting 40 mg, sampled by a unique portion of weave;
*the laboratories will receive other two samples, evidently different from the original one, therefore we rely on the sincerity of the laboratories;
*the samples will be deliver to the representatives in Turin;
*each operation will be filmed;
*there will not be any confrontation between the results until the results themselves will be defined as definitive.The definitive protocol showed effectively some differences between the original and the Turin's one too. This causes the protest of Gove and other scientists, that continue to criticized the sampling from a unique part of the cloth. If the chosen part would have been contaminated by external agents, every result would have been altered.As it's shown in the protocol the blind test is also vanished by the easy identification of the original piece.

The exam's dynamics

April 1988:the sampling

The sampling took place on 21 April 1988 in the Cathedral of Turin and was performed by Franco Testore, professor of weaves, and by giovanni Riggi di Numana, producer of biological equipments. The first performed the weighting operations while the second made the effective cut. As public there was also the cardinal Ballastrero, four priests, Luigi Gonella, photographers, the camera operator, Michael Tite and the laboratories' representatives (that according the protocol should not have been present): almost 30 people in total. While the protocol stated a sample of almost 1x7 cm, Testore proposed to cut a sample of the double measure, conserving a half in an insulated container in case of loss for the real one. So it was cut a piece of 81x21 mm, from which was discarded a stripe showing coloured filaments of doubt origin. The sample remaining of 81x16 mm, which weighted 300 mg, was firstly divided in two equal parts and finally one of them was cut in three samples, destined to the three laboratories.Were also divided among the laboratories three control samples (one more than those originally stated), that were:
*a fragment of weave coming from an Egyptian burial, discovered in 1964 an already dated to 1100 A.D.;
*a piece of mummy bandage dated back to 200 A.D.;
*some yarns sampled by saint Luigi d'Angiò's cloak, conserved in Saint Maximin, Var, France, dated back to 1290 and 1310.The Shroud's pieces and the control ones were inserted in nine metallic cylinders in order to perform the blind test.The dating of the control pieces, originally destined to remain unknown, was unfortunately published by Osservatore Romano on April 23rd.The scarce care used in the whole operation, the numerous protocol's violations and the differences in the quantities stated (weight of samples, dating and so on...) caused not only criticisms and polemics but also increased the suspects around a plot.The blind test was afterwards defined a "staging" by Evin and a "façade for public opinion" by Tite.

May-August 1988

The laboratories, which according to the protocol, should have worked separately and simultaneously, operated on the contrary one after the other (Tucson on 6 May, Zurich on June and Oxford on 8 August), interchanging information. In fact, according to the newspaper L'Avvenire published on 14 October the directors of the three laboratories met secretly in Switzerland: the admission of this will be published by the same directors.On 18 May the BBC entered in the Zurich laboratory in order to film the opening of the cylinders and once again were publicly declared the dating of the control samples.On 27 July the registration was transmitted. In that occasion was claimed that "the Shroud is medieval", while the Oxford laboratory had still to start the exams.On 26 August the English newspaper Evening Standard published a Shroud dating to 1350. The day after and on 28 September as well, Gonella denounced these heavy protocol violations.On 28 September Tite communicated the results to the Diocese of Turin and successively to Rome.

13 October 1988: the results are officially announced

On 13 October 1988 in a press conference the cardinal Ballastrero announced the results: the radiocarbon had provided a dating between 1290 and 1360, with a reliability percentage of 95%. The dating is back to the first historical documentation of the Turin Shroud.Yet two days after [David Sox published the book "The Shroud Unmasked": clearly the edition had been written before the announcement of results.The scientific official report was published after some months on "Nature". In detail the Tucson laboratory calculated a date of 646±31 years, Oxford 750±30 and Zurich 676±24; from which is easy to obtain a mid-range of 689±16 years. Applying the necessary calibration this date is converted in 1237-1288 with 68% of reliability and 1262-1384 with 95% of reliability.

uccessive events

These results, foreseen months before by the press, surprised many and had a world resonance. So far is still open a debate between those who declare, basing on the radiocarbon dating, the falsity of the Shroud and those who complain the unreliability of these exams.To these ones rapidly added the "plotters", that pretend to demonstrate a plot, clearly shown through the Tite's strange behaviour, the confusing sampling and the contradictions of those present, organised in order to create more mystery on the holy relic.From the days successive the announcement forth, many collaborators made interviews on press about the dating. Michael Tite, in a letter to Gonella dated to 14 September 1988, declared: "personally I don't believe that the radiocarbon dating demonstrated the Shroud is false [...] . The radiocarbon dating is not a proof in this sense". Evin, catholic, claimed that the holy Shroud belongs to a man crucified during Middle Age, though it's well known that in those times the crucifixion was not used any more.The Sunday Telegraph of 25-26 March 1989 talked about a donation of almost a million pounds offered to Oxford from "45 business men and rich friends" to thank the laboratories of having shown that Shroud is a medieval false. The donation was used for the creation of the Archaeology faculty and the rector became Michael Tite himself.On 4 June, in mysterious circumstances Timothy W.Linick, 42-years-old research of the Arizona University, committed suicide and there were voices of a murder, though it was never proofed.The documentary "Sindone, prove a confronto" ("Shroud, profs confrontation") in 2008 by David Rolf was an other retirement of the exams' executors: successive studies demonstrated that the quantity of carbon 14 on the weave could have been significantly modified by weather and bad conservation methods during the centuries. In the Shroud's case, basing on these new theories, could be sufficient a contamination of 2% to modify the dating from the real one to almost 14th century. Initially this thesis was introduced by media as credited by Cristopher Ramsey of the University of Oxford, who took part to the 1988 radiocarbon dating. Successively Ramsey said he was sceptic about a new radiocarbon dating.

Criticism to the exam dynamics

A list of criticism by scientists and journalists follows below.

Violation of protocols

Initially was stated that seven laboratories would have taken part using two different techniques, while were effectively chose only three laboratories using a unique technique. Zurich, Oxford and Tucson reached also the same conclusions communicating each other, interchanging results and opinions and violating the protocol followed.Has been criticized the false "blind test" as well and the announcement before the exams of the control pieces dating.

tatistic analysis

Some authors found some mistakes in the statistic data published on "Nature": the standard deviation obtained by Tucson is of almost 17 years, not 31 as published; the Chi-square distribution value is 8,6, not 6,4 and the relative significance level (which measures the reliability of result) is almost 1%, not 5% as published (in order to have an idea of how low is this significance level please notice that the control pieces' levels were 30%, 50% and 90%).As 5% is the minimum significance level acceptable, some experts claim that the radiocarbon result must be considered as irrelevant and must be repeated. Anyway many supporters of the exam reliability argue that all three results show a medieval dating.
Bryan J. Walsh examined each measurement through statistic methods, obtaining a probability of 95% that the three measurements would have been different. He also revealed that the carbon 14 level in the pieces sampled was not uniform, which confirm a possible contamination.

Accusation of samples' substitution

Some Shroud experts, basing on statistic contradictions, argue that the exams executors altered the results substituting the Shroud samples with original medieval pieces.According to Bonner-Eymard, the substitution was planned and happened in two parts:
*first Michael Tite (British Museum representative) provided a weave sample date back to 14th century;
*then the laboratories representatives changed the cylinders received with the false samples provided.The false samples, however, showed a dating more recent than expected (1400) and were manipulated in a way which caused the statistic anomalies. The original samples were those ones declared coming from the mummy.Among the proofs used by Bonnet-Eymard there's a photo showing the Tucson cylinder opened the day before the official opening.This reconstruction require the complicity of numerous people: Michael Tite and at least one person for each laboratory. The "plotters" raised doubts on Timothy Linick's death, who could have been murdered in order to keep secret the substitution.

Enrichment of carbon 14 percentage on the shroud by external factors

The cloth has been conserved for centuries in bad conditions, exposed to the candles' fumes (rich of carbonic dioxide), used as tablecloth for Mass. The cloth also risks to be burned twice: the first time in unknown date, the second one during the night of 3-4 Decemberwhen, when a burning destroyed the Saint-Chapelle of Chambéry where was conserved the Shroud.Some flames reached the cloth in different parts. The high temperatures of the burnings could have created molecular interactions between the weave and the carbon present in high density, while the silver relic container and the water used to cease the burning could have catalysed the enrichment of carbon. Nowadays, anyway, the catalysed enrichment is not yet scientifically proofed.

The Kouznetsov case

In 1944 the Russian scientist Dmitri Kouznetsov, a specialised biologist and archaeological chemist, announced to have proofed experimentally the carbon enrichment in ancient weaves in similar conditions and published between 1994 and 1996 numerous articles about this.The Russian expert's theories were spread and many Shroud experts basing on them showed the unreliability of the 1988 dating.Successively many scientists tried to reproduce the same Kouznetsov experiments, without obtaining similar results and this increased the number of experts doubting of him.Afterwards the professor Gian Marco Rinaldi discovered that Kouznetsov had never performed those experiments, inventing data and citing fonts and scientific unknown institutions (for instance do not exist the museums fro which he took the samples needed). Rinaldi also demonstrated the falsity of some other Kouznetsov researches that supported the creationist theory.In 1997 Kouznetsov was arrested in USA under accusation of receiving payments from some magazines interested in publication of false researches.

Sampling of unoriginal portion

In 2000, Joseph G. Marino and M. Sue Benford have raised the hypothesis that the sample used in the radiocarbon exam contained a portion of unoriginal weave (almost 60%): Margaret of Austria, aunt of Carl V, ordered in the last will that a portion of Shroud was donated to a church founded by herself. His will was performed by a maestro weaver that substituted the lacking portion with a medieval weave.In a 2005 published article Raymond Rogers argued that his chemical analysis confirmed this thesis: the sample used in the radiocarbon dating shows evident tracks of tincture, used in Middle Age to make the piece added similar to the Shroud colour.Is it possible that such a mistake could be made while none noticed it? It's interesting to notice that the piece sampled was chose only the day of the sampling, without analysis.Franco Testore , the cutter, had never seen the Shroud before and the laboratories experts sit at metres of distance.