Determination of the Age of the Shroud
Wojciech Kucewicz 
AGH University of Science and Technology, Kraków, Poland
Jakub S. Prauzner-Bechcicki
Jagiellonian University in Krakow, Poland
A separate problem that intrigues researchers is the age of the Shroud. Its documented history is known from 1356, when the crusader Geoffrey de Charny gave it to the canons in Lirey, France. Historians find ample evidence that the Shroud of Turin was known earlier as the Mandylion of →Edessa and then as a shroud kept in →Constantinople until it was looted in 1204.
Radiocarbon dating techniques are used to determine the age of objects made of organic materials. These involve measuring the content of the carbon isotope 14C in a collected sample. The amount of this isotope in living organisms is kept constant at a well-known level (1 isotope of 14C for every trillion carbon atoms of 12C) due to the process of carbon exchange with the environment that takes place in living organisms. In dead organisms, this does not occur and, under the influence of radioactive decay, the number of 14C isotopes gradually decreases. The half-life of carbon 14C is 5730 years. It is therefore sufficient to measure the 14Cisotope content to determine how long a sample has been dead. This method can be used to determine the age of the Shroud, but it is important to realise that this is an invasive procedure. The idea of carrying out such an analysis emerged immediately after the success of the research reported by the Shroud of Turin Research Project (→STURP) team. Already in 1982, this team proposed a second series of 26 different studies, including radiocarbon dating.
A not insignificant fact was the discovery of a new measurement technique by D.E. Nelson and C.L. Bennett (Nelson, Korteling, Stott 1977), who in 1977 proposed the use of Accelerator Mass Spectrometry (AMS) for radiocarbon dating. The advantage of this technique is the small sample mass (about 100 times less than in other techniques) needed for the procedure. This argument seems to be crucial in relation to such a unique cloth as the Shroud. Under pressure from laboratories possessing the AMS technique, comprehensive analyses were abandoned, and it was decided that only radiocarbon dating would be carried out, in three laboratories (Tucson, Zurich and Oxford), and the proven and experienced scientists of the STURP team were removed from this work.
The protocol of measurement principles was announced on 17 April 1988, and just four days later the Shroud samples were taken. This haste and inexperience caused chaos in the documentation. At the last minute, without considering the scientific arguments, it was decided to cut off a scrap of the Shroud from the upper left corner for analysis. Even a cursory analysis of the 1978 results seems to indicate that the sample was taken from the most unrepresentative area of the fabric.
The results were announced on 13 October 1988. All three laboratories determined the age of the Shroud to be between 1260 and 1390 (with a 95% confidence level) (Damon et al. 1989). This is roughly the time from which its documented history exists. This shocking information (research into the age of the Shroud was expected to point to the beginning of our era) immediately circulated throughout the world and was considered irrefutable proof that the extraordinary fabric was the work of a forger from the Middle Ages. Meanwhile, in the history of Shroud research, this is the study that most contrasts with the results of the overwhelming majority of other tests carried out both before and after 1988.
Unfortunately, an analysis of the documentation of the measurements and their results shows that the tests were not carried out with due diligence. According to the protocol of the measurement rules, the samples were to be tested by all laboratories at the same time with a prohibition on contacting each other. The analyses were to be carried out blind, i.e. three other samples of ancient linen were also prepared for parallel tests. Unfortunately, the laboratories performed the tests at different times, casting doubt on secrecy, while the control samples were easily distinguishable from the Shroud samples.
The publication describing the results, which appeared in the prestigious journal ”Nature” (Damon et al. 1989), was also not prepared with due care. Among other things, it lacks precise information on the weight of the samples and on their size. A cursory comparison of the results presented in Tables 1 and 2 shows a difference in the calculation of the measurement error (standard deviation) in determining the age of the Shroud by the Tucson laboratory. Based on the data in Table 1, it can be calculated to be ± 17 years, whereas the authors give a value of ± 31 years in Table 2. While the text does not explain the reason for this difference, it is important in the determination of statistical tests to confirm that the study sample is statistically homogeneous. The authors applied the χ2 test of concordance, the most commonly used test for such studies, obtaining a result of 6.4. On the other hand, if the measurement error calculated from Table 1 had been taken into account, the result would be 9.1. The first of these values allows us to conclude that the probability of dispersion in the measurement results is random and is 5%. This is the minimum value accepted for statistical tests. In comparison, the probability that the dispersion of the measurement results is random for the three control samples was 90%, 50% and 30% (Damon et al. 1989). Meanwhile, if the χ2 value determined from the data in Table 1 had been used for the calculations, this probability would have been about 1%, and therefore below acceptability. This leads to the conclusion that averaging the age of the Shroud on the basis of the results obtained in the three laboratories is statistically unjustified. The samples examined are not homogeneous in age. This was observed by Brain Walsh (Walsh 2000), who showed that the result of radiocarbon dating depends linearly on the distance measured from the edge of the Shroud. The age of the samples decreases linearly as a function of distance from the edge of the fabric.
A very important factor that may have affected the results of radiocarbon dating is the location from which the samples were taken for examination (the upper left corner of the fabric). The researchers point out that this is the area that was touched every time the Shroud was exposed. Grease and dirt from the hands may have caused more degradation of the linen. There has been a hypothesis that this area may have been repaired during the restoration of the cloth after the fire of 1532 (Benford, Marino 2008). The repair would have consisted of weaving in additional cotton threads in this area, which were in fact observed. Indeed, analysing the images taken in different spectra by the STURP team, it is clear that the sampling location differs from other parts of the linen. John Morgan (Morgan 2012)], on the basis of a digital analysis of the fluorescence images, showed that the sampling area for radiocarbon dating and the reference area from the central part of the Shroud are not statistically similar. In contrast, analysis of the X-rays showed that at least part of the sample was taken from an area that differed in weft pattern and density (Whanger, Whanger 2005).
If one were to assume that the samples were contaminated with younger biological material, e.g. during the 1532 reparation, this would have to account for 60–65% of the sample. No research confirms this. Perhaps if the samples had been taken from a different area of the Shroud or different sites, as suggested by the STURP team, the radiocarbon dating result would have been quite different.
The weaknesses described above in the selection of samples for radiocarbon dating, as well as in the statistical analysis of the results, lead to the conclusion that the results of the 1988 study can hardly be considered reliable. Unfortunately, the manner in which radiocarbon dating was carried out has restricted scientists’ access to the direct examination of the Shroud. Further work is only being carried out on the samples that were taken in 1988. The articles published in 2020 (Walsh, Schwalbe 2020; Di Lazzaro et al. 2020) not only summarise the reasons why radiocarbon dating does not meet modern accuracy requirements, but also propose a control check using this method for the age of the Dutch linen and charred (during the 1532 fire) fibres that were removed from the Shroud in 2002.
Since then, attempts have been made to find other methods that could determine the age of the Shroud. Raymond Rogers, a member of the STURP team, studied the vanillin content of flax fibres, which depends on the age of the sample and the temperature at which it is stored (Rogers 2005). This content decreases until it disappears completely. According to his estimates, the decomposition of 95% vanillin occurs at 20ºC after 3095 years, at 23ºC after 1845 years and at 25ºC after 1319 years. Examining the fibre fragments from the Shroud, he did not find vanillin there, whereas he discovered it in samples of other fabrics from the medieval period. It can therefore be concluded that the Shroud must be much older than medieval fabrics.
Another method of investigating the age of ancient linen fabrics was proposed by →Giulio Fanti of the University of Padua (Fanti, Malfi 2014; Fanti, Basso 2017). He collected a dozen samples of linen fabrics whose age was known. Using microscopic examination, he checked the surface quality of the threads and fibres, in particular surface deterioration and impurities, in order to exclude those samples that were significantly different from the others. In this way, he created a basis for the determination of calibration curves of various fibre properties as a function of time. Above all, he analysed the strength properties of the fibres, rightly assuming that the strength of the fabrics would decrease with age. Giulio Fanti studied several strength parameters: the Young’s modulus at increasing and decreasing stress, a parameter that determines the elasticity of the fibres, the loss factor at increasing and decreasing stress, the ratio of dissipated energy to accumulated energy, and the tensile strength. The Italian scientist determined the relationships of these parameters in relation to the age of the samples, and then examined the same parameters for the fibres from the Shroud and thus estimated their age. The age of the Shroud determined from these analyses is between 14 BC and 534 BC (at a 95% confidence level) (Fanti, Malfi, Crosilla 2015).
Giuilio Fanti, using his collection of ancient textiles, proposed another method for investigating the age of textiles, using Fourier Transform Infrared Attenuated Total Reflectance (FT-IR ATR) spectroscopy, which allows the absorption spectrum of infrared radiation by the material under study (e.g. linen cloth) to be determined (Fanti, Malfi, Crosilla 2015; Fanti et al. 2013). From the shape of the spectrum, the types of atomic bonds present in the sample can be determined. It was observed that the intensity of some areas of the spectrum decreased with the age of the fabric, while others increased. By determining the ratio of the area of these bands, it is possible to define parameters that change as a function of time. The time dependence of the defined parameters created in this way can be used as a calibration curve to determine the age of linen cloths. Fanti used the same method to determine the age of the Shroud. According to this study, the fabric dates from between 650 BC and 150 BC (Fanti, Malfi, Crosilla 2015).
The third method proposed by Fanti and his co-workers was the use of Raman spectroscopy (Fanti, Malfi, Crosilla 2015; Bonizzoni et al. 2016), which involves measuring the radiation resulting from the inelastic scattering of photons on the particles of the sample under examination. Here again, it can be observed, as in the previous method, that certain bands of the observed spectrum change their intensity depending on the age of the sample. The age of the Shroud determined with this method is between 370 BC and 430 AD. The combination of both optical methods, FT-IR and Raman spectroscopy, makes it possible to determine the time of the fabric’s origin between 172 BC and 452 AD, while the result obtained with the method based on fibre strength measurements (combined optomechanical method) finally establishes the age range of the Shroud at 120 BC and 292 AD (Fanti, Malfi, Crosilla 2015).
The new methods of measuring the age of the Shroud are not very accurate as yet, but they clearly indicate a time interval that is more consistent with other studies of the linen. Given the rapid progress currently being observed in the development of research techniques, it is hoped that it will be possible to reliably and non-invasively re-examine the age of the Shroud in the near future.
References
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Source of Image
1. Kim jest Człowiek z Całunu? [exhibition brochure], Kraków 2012