Few religious relics have been examined, challenged and argued over as intensely as the Shroud of Turin.
To believers, the centuries-old linen may be the burial cloth that covered Jesus Christ after the crucifixion. To skeptics, it remains an unresolved historical puzzle whose origins have long split scientists, theologians and historians.
Radiocarbon tests carried out in the 1980s suggested the Shroud dated to the medieval period. Yet some researchers continue to point to other features of the fabric, particularly the blood markings, as evidence that the story may be more complicated.
One persistent question has fueled doubt: if the cloth already bore the striking image of a crucified man, why is no such image described in the Bible when the disciples found linen in the empty tomb?
A new opinion paper now offers a possible answer, suggesting the image on the Shroud of Turin may not have been visible at first and could have appeared only later as the linen aged naturally or was exposed to heat.
Dr Kelly Kearse, an immunologist who has studied the Shroud extensively, pointed to experiments indicating that low-level radiation can change linen fibers without producing immediate discoloration. Under that scenario, a hidden or “latent” image might become visible only after time passed or the cloth was heated.
In those experiments, stronger laser pulses caused instant coloration but also damaged or vaporized bloodstains. Weaker pulses, by contrast, left the blood largely unaffected while creating an image that surfaced later.
Kearse said the idea could help account for two longstanding mysteries: the Shroud’s seemingly intact bloodstains and the absence of any biblical reference to a visible body image on the burial cloth. He stressed, however, that the proposal remains speculative.
Critics have also questioned why the mysterious image of a crucified man was never mentioned in the Bible when the disciples discovered linen inside the empty tomb
The 14-foot-long Shroud of Turin is believed by some to have wrapped Jesus’ body after the crucifixion and bears the faint, bloodstained image of a man with his arms folded in front of him.
The Bible describes linen cloths lying inside the empty tomb alongside a separate, folded face-cloth, but makes no mention of an image of Jesus’ face or body.
Researchers have proposed several explanations for how the image formed, including that it was created by an artist, caused by a natural chemical reaction or imprinted by a burst of radiant energy.
The radiant-energy hypothesis is popular among some supporters of the Shroud’s authenticity, but scientists have not established that such energy created the image or identified where it could have come from.
The theory suggests the image would have formed almost instantaneously. But if it appeared immediately, why did the Bible never mention an image on the burial cloth?
Skeptics say that omission supports the argument that the Shroud was created centuries later.
That view was strengthened by tests conducted at three laboratories in 1988, which dated the sampled material to between 1260 and 1390.
Some researchers have challenged those results because the samples all came from one small area of the cloth and produced variations that appeared to correspond with their distance from its edge.
The shroud first appeared in 1354 in France. The Church has treated it as an object of devotion but has not officially authenticated it as Jesus’s burial cloth. Pictured, the burial cloth was on display in 1998 in the Cathedral of Turin for the first time in 20 years
They argue that the tested strip may not have represented the entire Shroud.
However, the new paper, published on August 12 in the Journal of Historical Archaeology & Anthropological Sciences, considered another possibility: The image may initially have been invisible before gradually appearing as the cloth aged or was exposed to heat.
Kearse noted that Samuel Pellicori, a member of the scientific team that examined the Shroud for five days in 1978, was the first to suggest that the image may have emerged later.
Pellicori proposed that natural substances from the body, such as skin oils or burial ointments, were transferred to the linen and slowly caused its fibers to discolor.
This process is known as ‘latent coloration.’ The changes needed to create the image begin immediately, but the image does not become visible until the fabric ages or is exposed to heat.
Scientist Ray Rogers, who also participated in the 1978 investigation, suggested that a natural chemical reaction between substances from the body and the cloth could have produced the image.
He recreated linen fibers that resembled those on the Shroud and also believed the image may have developed gradually.
Kearse pointed to another unusual feature of the Shroud: The image rests only on the uppermost surface of the linen, affecting the top two or three fibers of its threads.
Each fiber is approximately 10 times thinner than a human hair, making the image extraordinarily shallow.
The Shroud of Turin Research Project (STURP) team used X-rays, ultraviolet and infrared photography, chemical analysis and microscopic tests to study the cloth’s fibers, stains and image (pictured)
Scientists previously used extremely short ultraviolet laser pulses to recreate some of the superficial discoloration seen on the Shroud on pieces of linen.
The experiments reproduced certain physical characteristics of the markings, rather than the Shroud’s complete body image.
When researchers used pulses powerful enough to produce an immediately visible mark, the energy damaged or vaporized bloodstains placed on the fabric.
That presented a problem for the energy theory because the Shroud’s bloodstains appear to have survived without suffering comparable damage.
If the cloth genuinely covered Jesus, Kearse argued, the blood would have been transferred onto the linen before the body image formed.
Any burst of energy responsible for creating that image would therefore have had to discolor the exposed linen without destroying the blood already covering parts of it.
Researchers found that the blood remained relatively unharmed only when they reduced the laser energy to much weaker levels.
Those weaker pulses altered the linen but did not produce an image that could immediately be seen.
Instead, the discoloration became visible after the material was heated or allowed to age naturally.
Later experiments involving both blood and serum produced similar findings, according to Kearse.
Even some of the weaker laser settings disturbed the stains, while only the lowest levels left the blood apparently undamaged.
Kearse argued that the results supported a possible sequence of events: Blood first reached the burial cloth, a weak burst of energy then altered its exposed fibers, and the resulting body image emerged sometime later.
That scenario could explain why the image did not destroy the bloodstains and why the disciples may have seen only apparently blank linen inside the tomb.
However, Kearse acknowledged that the evidence was indirect and did not prove that radiation formed the Shroud’s image.
The experiments were conducted on modern linen samples rather than the Shroud itself, and researchers still do not know what created its mysterious markings.
Kearse also said it was impossible to determine exactly when a dormant image might have become visible.
Natural, chemical or artistic explanations remain possible, and the proposed delayed-image process would require further experimental evidence.
The findings did not establish that the Shroud covered Jesus, that radiation created its image or that the markings developed after the cloth was removed from the tomb.
Kearse described the proposed sequence as hypothetical and said further evidence would be needed to demonstrate how, or when, the image formed.
