A following an article by De Caro et al., published in Heritage2022, 5, 860-870, many people ask us if it is possible to date the Shroud by this method as an alternative to 14C . This question was answered by Marco Ricci, Paolo Di Lazzaro and Alfonso Sanchez Hermosilla, Members of the Scientific Committee of the International Center for Shroud Studies, and published in the journal Sindon, at the following link:
In the article, which we publish below, they explain why X-rays are not useful for dating tissues, they only measure the mechanical deterioration of the cellulose of the tissue, but this does not allow us to establish a chronology, nor the age of the tissue.
Comments on the paper by De Caro et al., X-RAY DATING OF A TURIN SHROUD’S LINEN SAMPLE, Heritage 2022, 5, 860-870
The need for a more compact technology with lower costs than AMS devices used for C-14 radiocarbon dating of fabrics has encouraged several laboratories to develop alternative dating methods that can correlate textiles' age with chemical or physical changes in cellulose. Actually, vegetal fibers, such as cotton or flax, are made of cellulose which, in its turn, consists of long, linear chains of sugar units. Over time, by aging, these long chains are degraded and undergo several breaks due to the effect of temperature, humidity, handling, friction abrasion, etc., so that their length is considerably shortened. Should this shortening occur at a constant rate, the age of a textile might in principle be estimated by measuring the extent of its fibers' degradation.
In this frame, a couple of years ago, De Caro et al. showed how a particular use of X-rays (Wide-Angle X-ray Scattering, or WAXS) can provide a way to measure the degradation of cellulose fibers and, after calibration with several reference samples, to date ancient textiles (De Caro et al., X-ray dating of ancient linen fabrics, Heritage 2019, 2, 2763–2783, impact factor not available). More recently, the same research team has used this technique to date a small sample from the Turin Holy Shroud of which neither the origin nor the "chain of custody" is specified (De Caro et al., X-ray Dating of a Turin Shroud’s Linen Sample, Heritage 2022, 5, 860-870, impact factor not available). The result would contradict those o is f the 1988 radiocarbon dating and would be compatible with the hypothesis that the Turin Shroud is a 2000-year-old object.
Should we trust the results of this paper?
The method developed by De Caro et al. relies upon the occurrence of modifications of the textile samples. As the authors discuss in their 2019 paper, the aging of textiles can occur via several pathways including thermal, hydrolytic, photochemical, oxidative, and enzymatic ones. As a consequence, the rate of these modifications is strongly influenced by environmental conditions, e.g., temperature, humidity, partial pressure of oxygen, exposure to sun-light, presence of possible catalysts such as acids, bases or metals, storage, handling conditions, and, finally, presence and activity of microorganisms. Thus, it seems unlikely that the method can provide an absolute clock as reliable as that based on radio-carbon decay which, as far as we know, is not affected at all by any environmental condition.
Moreover, looking at Figure 2 of the 2022 paper, it is clear that small differences in the WAXS profiles correspond to large differences in the textile's ages. Also taking into account some subjectivity of the rescaling/calibration process (dealt with on page 863 of the paper), an accurate age estimation ap-pears controversial, to say the least.
The application of the WAXS technique to the Shroud also appears problematic because of the possible effect on cellulose degradation of the fire that the Shroud suffered in 1532: any accelerated degradation would, indeed, increase the apparent age of the textile. De Caro and co-workers address indeed this point but their discussion, although clear, is probably simplistic. According to them, hydrolysis (i.e., reaction with water) would be almost the only process responsible for cellulose degradation. Since during a fire, the partial pressure of water is reasonably very low, no significant degradation of the Shroud fabric should be expected due to the 1532 fire. In this view, any possible role of, e.g., thermal degradation completely neglected.
In addition, the considerations of De Caro et al. about the low humidity present on the Shroud dur-ing the burning of its case might be far-fetched. Inmediately after the extraction of the Shroud cloth, which was at a temperature likely close to 200 °C with molten metal droplets piercing the fabric, water was thrown on the cloth to stop the spread of the flames. The humidity experienced by the wet cloth was 100% and the temperature of the fabric was still very high: linen is a fabric that heats slowly and just as slowly cools. As a result, the "low humidity" scenario assumed by De Caro and co-workers was probably not verified.
For sure, a significant amount of further experimental work is needed to check whether the high temperatures suffered by a wet cloth may increase or not the degradation of cellulose fibers.
In conclusion, it seems that the WAXS method is suitable for dating samples that have been stored under reasonably stable conditions, such as in sealed underground tombs, without having experienced fluctuations in humidity and temperature, nor exposure to sunlight, nor handling. The method is probably worth to be verified in different laboratories. On the other hand, it remains unclear whether the WAXS technique can be reliably used to date the Shroud, which suffered from flames and water and, in addition, has been subjected to completely unknown handling and storage conditions over the centuries. However, even if the method reliability should be confirmed, new tests on other Shroud samples would be necessary to support the very first result so far obtained on just a 0.5 x 1 mm sample.
Anyway, the path toward an alternative tissue dating technique to C-14 that is nondestructive and yields accurate results is fraught with difficulties but is worth pursuing.
Marco Ricci; Paolo Di Lazzaro; Alfonso Sanchez Hermosilla;
members of the scientific committee of the International Center for Studies on the Shroud
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