Tested on the Turin Shroud, it is based on a new principle compared to current techniques
Dr. Liberato De Caro is a scientist at the Institute of Crystallography of the National Research Council (CNR), who has been developing and applying innovative techniques in materials science for years. In recent years, he has participated in research on the Turin Shroud, a fabric believed by some to be the cloth in which the body of Jesus Christ was wrapped. The Shroud was dated using the radiocarbon technique in 1988, but this dating has been scientifically contested.
Dr. De Caro worked on a new dating technique called Wide-Angle X-ray Scattering (WAXS), which allows for non-destructive analysis of the chemical composition and structural properties of materials. The scientist’s team applied the WAXS technique to a sample of the Shroud fabric, with the aim of determining its age and authenticity. Their research has raised significant interest and debate in the scientific community.
What is the basis of this new technique?
X-rays are useful for measuring the order and structural degradation within things. For example, we use X-ray radiographs to assess the state of order of our bones and joints, to check for degradation (osteoporosis), fractures, etc. The WAXS technique allows us to evaluate the order of the material and the degradation of microscopic structures up to the atomic scale. With regard to textile fibers, they contain cellulose, formed by the repetition of the same molecule, which presents itself in long polymer chains. Over the centuries, these polymer chains of cellulose break down, becoming shorter on average. This degradation of cellulose, which depends on relative humidity and ambient temperature, is a natural process that we can define as natural aging of cellulose. The WAXS technique allows us to evaluate, within the vegetable fibers of the threads that make up archaeological finds, to what extent the polymer chains of cellulose have shortened on average, and therefore to calculate how much time has passed.
How does the WAXS technique work?
Every new dating technique starts from the determination of a calibration curve, obtained from dated samples. The unknown sample is compared to this calibration curve, and in this way, we determine how old the new sample under examination is. Similarly, the radiocarbon dating technique works. Analogously, we proceeded with the new WAXS dating technique. In particular, a series of ancient linen samples of different epochs, already dated using carbon-14 or of known age for historical constraints, were dated using the WAXS technique, obtaining a calibration curve for the new dating technique.
Why is it important?
Textile samples have a microscopic structure with about 50% of the space between microfibers that is empty, filled with air or dirt, contaminants. For this reason, radiocarbon dating, which works very well for samples with a very compact microscopic structure or for textile samples preserved in isolation, such as the bandages of Egyptian mummies, may not work with textile samples from archaeological finds not preserved in isolation. Indeed, the less compact microscopic structure of the samples to be dated may favor excessive contamination with carbon from later epochs, which is not always completely removable with standard cleaning techniques, falsifying the final result. The Turin Shroud, for its religious importance, has been at the center of the veneration of the faithful and, consequently, has certainly undergone a high level of contamination, which has compromised the radiocarbon dating performed about 35 years ago, when, among other things, the protocols for cleaning samples to be dated were not yet standardized as they are today. The WAXS dating technique, instead, is not afraid of contamination, as it is based on physical properties of the material under examination that are completely different, and can therefore be considered a useful alternative to radiocarbon dating precisely on textile samples.
What are its advantages?
It is sufficient to have a sample with dimensions even smaller than a millimeter for the WAXS dating technique. Instead, for radiocarbon dating, the samples must be larger. Finally, the new dating technique is non-destructive, and the sample can be dated multiple times and by different laboratories. In radiocarbon dating, the sample subjected to analysis is destroyed, and therefore, to repeat the dating, it is necessary to take new samples. Clearly, every new sampling from an archaeological find is a small part of it that will be lost forever. These, just described, are the advantages of the WAXS dating technique compared to radiocarbon dating.
What are its limitations?
If the textile fibers have undergone a process of aging not only natural, linked to the mean secular temperature and relative humidity of the places and locations where the archaeological find has resided, but also actions of acidic, basic, enzymatic, microorganism, insect, etc. substances, then the WAXS dating technique cannot be used to determine the age of the find. The optical microscope analysis can, however, show the integrity of the textile fiber structure, typical of natural aging, before dating. Indeed, aggressive chemical substances or microorganisms, if they attack cellulose, also deteriorate the structure of textile fibers and threads, and it is easily noticeable under the optical microscope. In any case, even if an archaeological find has undergone, for example, aggressive actions of acidic substances, it may still have intact parts that have undergone natural aging, which can be easily identified by inspecting the sample with a magnifying glass. In this case, the sample should be taken from the area of the textile that does not show signs of structural damage to the fibers. The optical microscope analysis would also confirm the eventual integrity of the sample taken, before being subjected to WAXS dating.
What were the results on the Shroud?
The determination of the calibration curve for the WAXS dating technique was published in a first scientific work (https://www.mdpi.com/2571-9408/2/4/171).
Then, the work of dating the Shroud sample was published (https://www.mdpi.com/2571-9408/5/2/47). The comparison of the results obtained on the Shroud sample with the calibration curve obtained from the series of ancient linen samples of different epochs, allowed to date the Shroud, showing that the sheet should have 2000 years of history, overturning the response of the radiocarbon dating, which had indicated the archaeological find as a possible medieval fake. Even the direct comparison of WAXS measurements with those obtained from a sample taken from the fortress of Masada, which fell into the hands of the Romans in 74 AD, with a sample, therefore, that certainly has 2000 years of history, allowed to confirm that the Turin Shroud is also ancient 2000 years, independently of the comparison with the calibration curve.
Subsequently, a third work was published, to try to reconstruct, based on the determination of the natural aging of linen, where the Shroud might be in its hidden history, before arriving in Europe (https://www.mdpi.com/2078-2489/13/10/458). Indeed, the natural aging of linen depends on the mean secular temperature and relative humidity of the places where the Shroud was preserved. Too hot locations would have accelerated the natural aging of linen too much. Too cold locations would have delayed it. For this reason, by comparing the value of the natural aging of linen measured on the Shroud sample with that calculated for some locations where the Turin Shroud might have been preserved (Jerusalem, Memphis, Beirut, Edessa, Camulia, Constantinople, etc.), based on historical information we have on the acheiropite images of Christ’s face, we can have very interesting historical indications on where the Turin Shroud might have been kept and venerated in the first 13 centuries of Christian history, before its arrival in Europe. For example, if a man lived in Africa, he would have a very tanned skin and the sun, in the long run, would produce deep wrinkles on his face. If the same man lived, instead, at the North Pole, his skin would be much paler and might have lesions due to exposure to very low temperatures. Therefore, by looking at this man’s face, we could make hypotheses on where he lived or is living. Similarly, the level of structural degradation of cellulose varies depending on the geographical region, and this allows us to make concrete hypotheses on the locations where the Shroud might have been kept in the past. In this way, the theoretical analysis of cellulose degradation can become a useful tool for historians, providing them with a tool for verifying the hypotheses advanced.
Finally, the analysis of the structural degradation of cellulose allows us to evaluate whether the archaeological find is preserved in optimal conditions to preserve its integrity in the centuries to come, suggesting values of ambient temperature, composition of controlled atmosphere of any storage lockers, and relative humidity suitable for its conservation.
