The Holy Shroud (Syndone) and Carbon 14 dating: what was actually measured in 1988?

The 1988 Carbon-14 continues to be cited as evidence against the Turin Syndone. But what does the original radiocarbon dating data actually show?

A is a linen burial sheet kept in the Turin Cathedral.

In Portugal it is sometimes referred to as Holy Shroudalthough this name more correctly corresponds to the cloth preserved in Oviedo which, according to tradition, covered the head of Jesus of Nazareth.

The Turin burial sheet presents the front and back image of a man with marks compatible with an execution by crucifixion.

Introduction

Year 1989, the British scientific magazine Nature the results of radiocarbon dating carried out the previous year on the Turin Syndone. The analysis indicated that the tissue fragment studied had a calibrated date located between the years 1260 and 1390.

Disclosure of results had a brutal impact worldwide in public opinion and has often been interpreted as a definitive determination of the age of the burial sheet.

However, decades later, several researchers returned to critically examine both the experimental protocol and the data obtained.

The scientific debate that developed later did not focus on validity of the carbon 14 method itself, but under the conditions in which it was applied to the Turin Syndone and the representativeness of the sample used.

It therefore becomes absolutely essential to understand what really was measured in 1988as this requires distinguishing between the robustness of the scientific method and the limitations of the experimental plan adopted in that particular case.

So what does carbon-14 dating actually measure?

One frequent error in the public debate consists of stating that carbon 14 dating directly determines the age of a historical/archaeological object. The method measures the age of organic material analyzed.

In living organisms, the carbon present in tissues maintains a relatively constant proportion between carbon 12 (stable) and carbon 14 (unstable) isotopes, since these interact with the atmosphere through biological processes.

When the organism diesthis exchange ceases and the concentration of carbon 14 starts to decay (decrease) progressively at a known rate.

In the case of a linen fabric, such as that from the Syndone of Turin, radiocarbon dating determines approximately the time at which the linen plant stopped exchanging carbon with the atmospherethat is, the period in which it was harvested to produce the fibers that make up the fabric.

Thus, the interpretation of any radiocarbon date always requires a careful and contextual analysis of the studied object ().

The experiment carried out in 1988

In April 1988 it was withdrawn a small fragment of tissue from a peripheral region of Syndone. This sample was later divided between three specialized laboratories: the University of Arizona in Tucson, the University of Oxford and the Federal Institute of Technology in Zurich.

The process was coordinated by the British Museum.

Sample representativeness

Initially, the protocol proposed for dating provided for the collection of samples from different regions of the fabric. However, the final protocol ended up being simplified and the dating of Sindone de Turin was based and focused solely on a sampling area located in a peripheral region of the tissue.

From the point of view of archeometry and scientific metrology, the representation of the sample constitutes an essential element, since the validity of any measurement depends on the analyzed fragment adequately representing the entire object.

Thus, if the sample used is not representative of the object as a whole, the result obtained applies only to the analyzed fragment and not necessarily to the artifact in its entirety.

Further chemical analyzes

In 2005, the chemist Raymond N. Rogers in the magazine Thermochimica Actaa comparative analysis of fibers from the dated area and other regions of the Syndone of Turin.

Rogers identified significant chemical differences between these fibers, including the presence of cotton and coloring substances in the area used in dating, which suggests that the area used in dating may, in fact, not be fully representative of the rest of the burial sheet.

Metrological assessment

Scientific metrology establishes fundamental principles to evaluate the quality of a measurement. To ensure reproducibility of results and reduce the influence of potential error factors, it is necessary to properly calibrate measuring equipment, validate the technique used and verify experimental conditions

The objective of these quality controls is not only to eliminate the possibility of failures, but also detect potential sources of error and critically analyze the results obtained, applying tools such as measurement uncertainty estimation.

Some of these methodological aspects have also been discussed in recent scientific communications dedicated to the analysis of the radiocarbon dating of the Syndone of Turín, such as the presentation “A Fallacy to C-14” held in Cieza, Spain, by Antonio Petitmember of EDICES – Research Team of the Spanish Center for Sindonology, based on the work of several researchers in this area.

Statistical significance

A homogeneity test in the statistical treatment published in 1989 to assess the compatibility between results obtained by different laboratories. THE probability value obtained was approximately 4.1%.

In experimental statistics, for determinations using C-14, a conventional threshold of 5% to assess data compatibility. The fact that the value obtained is slightly below this limit suggests that the dispersion between laboratory results may be higher than expected for a perfectly homogeneous sample.

Gradient in the dates obtained

Some researchers also observed that the dates obtained by different laboratories, presented a progressive variation over a few centimeters of the sample (7 centimeters wide from one end to the other, by three and a half in height) analyzed, which may suggest the presence of heterogeneity in the same (sample).

The results of carbon 14, analyzed mathematically, do not point to a homogeneous or solid dating for the Turin Syndone as a whole, but rather to a sample collected in a peripheral area with anomalous behavior and not very representative of the complete sheet.

In a range of less than 7 cm, the same laboratory, Arizona, varied its results in 192 years between one sample and another, while Oxford and Zurich, with points separated by only about 2 cm, showed a 130 year difference.

This strong internal gradation, far from ending the debate, reinforces the idea that a truly representative part has not been dated of the tissue, but rather an altered peripheral zone.

In fact, the statistical extrapolation presented indicates that, if the sample had been collected approximately 50 cm more towards the centerpredictably the dating would have placed the sheet around the 1st century.

Modern statistical reassessment

And in this field, in 2019, Tristan Casabianca, Emanuela Marinelli, Giuseppe Pernagallo and Benedetto Torrisi in the magazine Archaeometry a statistical reevaluation of data from the 1988 experiment. The study concluded that the results present a statistical heterogeneity higher than expected for a homogeneous sample ().

Conclusion

Radiocarbon dating carried out in 1988 constituted a important episode in the history of the investigation into the Turin Syndone.

The carbon 14 method remains as a robust scientific tool and widely used in archaeology, although, for the exclusive study of tissue samples given the imprecision it presents, archaeologists currently prefer to complement them with other techniques.

Therefore, in the specific case of the Turin Syndone, several elements raised by subsequent studies suggest that the 1988 experience should be interpreted with extreme care with regard to the age of the entire tissue.

In scientific research, experimental results are continually reevaluated in light of new data and new methodologies in parallel with technological advancement. It is precisely this process of critical review that allows the progress of scientific knowledge.

In science and its debates, it is essential to distinguish different levels of evidence. Some elements correspond to directly observable facts and others belong to the domain of hypotheses or interpretations.

In any scientific experiment, the results depend on conditions in which the study is carried out and the representativeness of the sample analyzed.

Therefore, reducing the entire issue of the Turin Syndone to a single dating carried out on a small fragment of tissue, does not correspond to the real complexity of the problem.

In science and its investigations, the results were not, are not, and never will be final decrees, but stages of a continuous process analysis and review.