Evidence of Contamination
In 1988 when the radiocarbon dating took place, there was already a substantial amount of evidence which showed that the Shroud was much older than the age indicated by that test. However, carbon dating anomalies were not at all unusual and several archaeologists had previously warned of the risk of obtaining a misleading date from a rogue sample which had been affected by contamination.
Shortly after the publication of the Shroud test report in Nature, various scientists re-examined the published results and found some anomalies that caused concern. The three laboratories had run their tests using postage-stamp sized samples cut from a strip measuring approximately 81mm by 16mm which had been removed from a corner of the Shroud. This was one of the worst possible choices for the sample location as that corner had been handled excessively over the years when the Shroud was raised and stretched during public expositions. It was also a few centimetres away from a badly charred area and there were visible water stains in that area of the cloth.
Statistical Evidence of Contamination
The measurements made by the three laboratories, twelve in total, were unusual. It was to be expected that there would be minor differences between the results obtained due to random measurement errors but instead they indicated that the measured age increased along the length of the strip. Statistician Bryan Walsh produced a chart (see across) showing the individual date measurements made by each laboratory and the horizontal distance between the left edge of the cloth and the midpoint of their tested fragment. This revealed an age gradient, with the oldest results towards the left of the sample and the youngest towards the right. If, as suspected, some form of contamination had caused an enrichment of carbon-14 in the Shroud, it must have intensified with increasing distance from the left edge of the cloth.
Even the analysis published in the Nature test report stated that there was only a 5% probability that the difference in measurements obtained by the three laboratories was solely due to random variations. It therefore follows that there must be a 95% probability that another factor had affected the results obtained and the most plausible cause was the presence of some form of contamination in the samples tested.
There is no doubt that the Shroud’s chequered history had exposed it to several potential contaminants which could have changed the carbon-14 content of the cloth. In addition, the unknown process that had formed the image could also have affected the dating measurements.
In the years since the radiocarbon test, various scientists have attempted to explain how a first century linen cloth could have produced a medieval dating result. Most of these have unable to withstand close scientific scrutiny. However, there are two possible explanations for the dating anomaly which are supported by evidence revealed by Shroud research:
Medieval Repair. The corner from which the radiocarbon dating sample was taken may have been repaired by highly skilled 16th century weavers who were known to be capable of producing an ‘invisible reweave’. A mixture of original and medieval material in the sample tested would account for the 1260-1390 AD dating result.
Neutron Absorption. If radiation was released during the resurrection, it could have involved the release of neutrons, causing an increase in the amount of carbon-14 present in the Shroud. This increase would have caused the radiocarbon age measurement to give a much younger result than its true age.
Most of the scientists who have studied the Shroud tend to favour one or the other of these hypotheses. Both of them provide plausible explanations for why the radiocarbon date was completely incompatible with all the other dating evidence which shows the Shroud to be much older. They can also explain the age gradient which has been shown to be present across the sample area. However, in both cases the supporting evidence isn’t yet strong enough to be considered ‘proof beyind reasonable doubt’.
A future, detailed scientific examination of the Shroud could reveal new evidence that would help determine the true cause of the radiocarbon dating discrepancy. However, perhaps understandably, the Vatican appears to have no desire to allow any further scientific studies of this most sacred relic.
The following links provide further information relating to possible contamination of the Shroud
On Carbon Dating the Shroud. An article by achaeologist William Meacham published in BSTS Newsletter No. 14, September 1986.
Carbon Dating of the Shroud of Turin: Partially Labelled Regressors and the Design of Experiments. A paper by Marco Riani et al which provides statistical evidence of an age trend across the width of the tested Shroud sample (2010).
Statistical and Proactive Analysis of an Inter-Laboratory Comparison: The Radiocarbon Dating of the Shroud of Turin. A paper by Paolo Di Lazarro et al which provides statistical evidence of the presence of contaminents on the Shroud sample (2020).
