The Shroud is always at the center of international attention, being the most studied relic in the world. Among the most interesting studies are those conducted by ENEA and STURP
The STURP Investigations
In the 1980s, the group of American scientists STURP (Shroud of Turin Research Project) conducted a series of examinations on the Shroud between October 8 and 13, 1978, using visible and ultraviolet spectroscopy for reflectance and fluorescence, X-ray and IR spectroscopy, mass spectrometry, infrared thermography, radiography, and other advanced techniques.
The analyses confirmed the absence of pigments and dyes on the cloth and demonstrated that the body image is absent beneath the bloodstains, indicating that it formed after them. It was also established that the image is due to an oxidation-dehydration of the cellulose in the superficial fibers of the fabric, with the formation of conjugated carbonyl groups. This alteration is extremely superficial, with a depth of about one-thousandth of a millimeter.
The main results of STURP related to the study of the image are:
Spectroscopic, fluorescence, X-ray, thermographic, Raman spectrometry analyses and microchemical tests showed that the image is neither painted, printed, scorched by a hot bas-relief, nor obtained by rubbing on a sculpture.
The color is caused by an oxidation, dehydration, and conjugation of the cellulose in the linen fibrils. The fibrils in the image areas show accelerated aging compared to those in the areas without image.
The image shows a screening effect: the shading of the color does not depend on chromatic variation of adjacent fibrils, but on the number of colored fibrils per unit area, sparser in light zones and denser in dark zones.
The coloration contains three-dimensional information of the body. By associating a height value proportional to the chromatic intensity of the various zones, a proportionate three-dimensional reproduction of a human body is obtained. With traditional photographic images, the result is irregular and disproportionate.
The color is limited to a very thin layer of the outer wall of the linen fibrils, with a depth of about 200 nanometers (one-fifth of a thousandth of a millimeter). This type of coloration is impossible to achieve with conventional painting techniques or by heating a statue or bas-relief in contact with the fabric.
The reddish stains on the Shroud contain substances typical of human blood. However, a critical review of the studies conducted in the 1980s by STURP and Prof. Baima Bollone suggests that there is no absolute certainty regarding the species of the blood, making further analysis necessary.
In the samples analyzed, the image is not present beneath the bloodstains, suggesting that the blood may have shielded the fibrils from the process that generated the body image.
STURP concluded: “The image on the Shroud is that of a scourged and crucified man. It is not the product of an artist. The bloodstains are composed of hemoglobin and tested positive for serum albumin. The image is a mystery.”
The ENEA Studies
In 2005, a technical report from the ENEA Center in Frascati reported the launch of a study aimed at reproducing on linen fabrics a coloration similar to that of the Shroud image.
Using an excimer laser emitting in the far ultraviolet, researchers obtained results that reproduced the extreme superficiality of the coloration, the lack of fluorescence, the absence of coloration beneath the bloodstains, and the inverse relationship between the intensity of the coloration and the distance between the source and the cloth.
These studies did not explain the formation of the Shroud image, but helped improve understanding of it. The ENEA report stated: “No one can hypothesize that the image on the Shroud was produced by ultraviolet light flashes emitted by a laser. Our results show that the excimer laser is a powerful tool to simulate the physical and chemical processes that could have caused the coloration.” And the scientific and technological difficulties in reproducing the image make “the hypothesis of a medieval forger unreasonable.”
Both the ENEA and STURP studies have made it possible to establish precise scientific criteria for evaluating the reliability of attempts to reproduce the image. All theories proposed so far have proven to be incomplete: either they were not accompanied by rigorous experimental verification, or they produced images with physical and chemical characteristics different from those of the Shroud.
To this day, it is certain that no one in the Middle Ages could have reproduced it using the techniques available at the time, so it is not a forgery. We still do not know how the image was produced.
Paolo Botti
RESUME:
Hypotheses on the Formation of the Image
Natural theory: the image would have formed through chemical reactions between the body and the fabric, for example due to volatile amines (such as putrescine and cadaverine). However, this does not explain the extreme precision, the three-dimensionality, or the superficial nature of the coloration.
Thermal theory: contact with a hot body or a bas-relief. Discarded: it leaves burn marks and does not account for the microscopic details.
Pictorial theory: the proposal that it is a medieval artwork. Discarded by scientific studies: no traces of pigments or brushstrokes have been found.
Laser/intense light theory (ENEA): a high-energy UV light pulse could have simulated the effects on the fiber. However, it would require an enormous amount of energy, not achievable with medieval means (nor with modern ones on a large scale).
Paranormal or miraculous hypothesis: some propose that the image was formed supernaturally at the moment of the resurrection. However, this cannot be scientifically verified and remains within the realm of faith.
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