The age-old debate over the Shroud of Turin is being resurrected this Easter — thanks to the attention of a new pope, the creation of a "Shroud 2.0" app, and a new book that claims the cloth dates back to Jesus' time.

The claim immediately faced a wave of criticism, including a harsh statement from Turin's archbishop that some say has driven a stake into the book's heart.

Believers say the centuries-old shroud bears the imprint of Jesus, chemically captured in the cloth at the time of his resurrection. Skeptics say it's a cleverly done medieval fake, wrapped up in highly debatable scientific claims that just won't die.

The newly published Italian-language book — "Il Mistero Della Sindone," or "The Mystery of the Shroud" — recycles some of those claims, adds in some fresh results from single-fiber tests, and makes the argument that the shroud shows the difficult-to-reproduce image of a man who lived sometime between 280 B.C. and the year 220.

If that's not enough to bring the shroud back into the spotlight, there's also the news that Pope Francis, who was named to lead the Roman Catholic Church just last month, will appear on Italian TV on Holy Saturday to introduce a RAI Uno TV appearance of the shroud. "It will be a message of intense spiritual scope, charged with positivity, which will help (people) never to lose hope," the Italian ANSA news agency quoted Turin Archbishop Cesare Nosiglia as saying.

And then there's Shroud 2.0, a free app for Apple's iPad/iPhone (and soon for Android) that lets users zoom in on high-definition images of the shroud and get factoids about its history. The app is being offered by Haltadefinizione, which took photos of the relic in 2008 and collaborated with church officials on the project. Shroud 2.0 is being offered as an "evangelization tool," according to the Vatican's News.va website.

Antonio Calanni / AP file

A photo from 2000 shows the Shroud of Turin displayed at Turin's cathedral.

Scientific links
The Catholic Church has taken no official stand on the authenticity of the shroud, which is kept under lock and key in Turin and is only rarely brought out for public display. But over the years, some researchers have tried to show that the shroud goes back to biblical times rather than to the 14th century.

"The Mystery of the Shroud" is the latest book of this genre. It was written by journalist Saverio Gaeta and Giulio Fanti, an engineering professor at the University of Padua. Fanti is part of a controversial research group that has claimed the image on the cloth couldn't possibly have been created by natural means. The new book refers to those past claims, plus a new angle.

That angle has to do with single fibers that were purportedly vacuumed up from the shroud during scientific testing. Fanti and his colleagues put the fibers through a series of mechanical and chemical tests. "Combining the two chemical methods with the mechanical one, it results [in] a mean date of 33 B.C., with an uncertainty of plus or minus 250 years at 95 percent confidence level, that is compatible with the period in which Jesus Christ lived in Palestine," the publishers say in a news release.

Skeptical views
Fanti's claims drew a quick reaction from Joe Nickell, a research fellow at the Committee for Skeptical Inquiry who regularly counters claims from Fanti and other shroud researchers.

"As is typical of a religious rather than scientific agenda, their news was shrewdly released just in time for Easter," Nickell said in a blog posting. "That alone casts doubt on the claims, but there is more."

Nickell pointed out that Fanti's tests "involve three different procedures — each with its own problems — which are then averaged together to produce the result." He said that stands in contrast with 1988's mass spectrometry tests, which yielded a date range between 1260 and 1390. Fanti says those earlier tests were not "statistically reliable," but Nickell and most scientists are sticking with the verdict rendered in 1988.

As a professional skeptic, Nickell can be expected to voice doubt about the book. But criticism also came from Archbishop Nosiglia.

Because there's "no degree of security" as to the authenticity of the fiber samples, the shroud's custodians "cannot recognize any serious value to the results of these alleged experiments," Nosiglia said in a statement quoted by La Stampa's Vatican Insider. The archbishop's comments "put stakes into Fanti's work," Vatican Insider reported.

Somehow I suspect that shroud science is not truly dead, but what do you think? Feel free to weigh in with your own verdict in the comment section below.

More about science and the shroud:

• Was resurrection story inspired by cloth?
• Experts re-create the face in the shroud
• Cosmic Log archive on Shroud of Turin

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

The Shroud of Turin has been seen as many things over the past 620 years, ranging from true burial cloth of the risen Jesus to clever medieval fake, but Cambridge art historian Thomas de Wesselow puts together a 448-page-long case for one of the lesser-known theories in his new book, "The Sign": that the shroud's negative image of a naked, bloodied man was really produced by Jesus' decomposition, and that the stories of his resurrection were inspired by the display of that cloth to his earliest disciples.

"The message really is that the Shroud of Turin is authentic," de Wesselow told me. "This is the only rational way of understanding this image. It can be understood entirely naturalistically. There's no reason to invoke a miracle to explain the image."

De Wesselow acknowledged this could be a hard sell for believers as well as for skeptics. "There are two big things I am arguing against," he admitted.

He's already taking flak from both sides.

"It's breathtakingly astonishing," said Joe Nickell, a senior research fellow at the Committee for Skeptical Inquiry who has written extensively about the shroud. "He's clearly not a doubting Thomas. He's come up with some rather silly ideas, and then as people often do, he's fallen in love with them."

Meanwhile, in a column about the shroud, the Catholic Herald's Francis Phillips basically brushed off de Wesselow's views, saying they were "too eccentric to reproduce here."

Legends and lore for Easter
"The Sign" is the latest example of shroud lore that comes out during the Easter season, just around the time when millions of Christians are dwelling on the story of Jesus' crucifixion and resurrection. (I'm linking to other examples at the end of this item.) The Shroud of Turin has a clear line of provenance going back to around 1390, but when you try to go further back, you can easily get swept up in tales of the Knights Templar and legendary relics like the Veil of Veronica and the Holy Mandylion.

De Wesselow comes at the story from his background in art history. He's been researching the story of the shroud full-time for the past five years, and has woven together an explanation from scientific findings that seem to support the shroud's authenticity, plus perspectives on the animist beliefs of ancient peoples.

"I've studied images, what they mean and how they affect people," de Wesselow said. "In the old days, people saw images as potentially alive. They had potentially a consciousness. ... That type of thinking was absolutely standard before the modern age. It has nothing to do with an optical illusion, and it has nothing to do with people being stupid."

De Wesselow picks up on the idea that the shroud is actually a "vaporograph," colored by a chemical reaction between the gases exuded by a dead body and the carbohydrate deposits on the surface of Jesus' burial cloth. Blood stains were left on the cloth as well. When the shroud was taken from the body, the ghostly image remained behind — and de Wesselow said Jesus' disciples could have interpreted that image as the spiritual manifestation of their leader.

"The appearances of the risen Jesus were simply viewings of the shroud image," he said.

Here's what de Wesselow thinks happened next: After a series of viewings in the Holy Land, the shroud was and taken to the city of Edessa in modern-day Turkey, where it came to be folded up, framed and venerated by the Byzantine Christians as the Mandylion. The cloth was transferred to Constantinople in the 10th century, and disappeared in the year 1204, only to turn up again in France in the 1300s. The shroud was transferred to Turin in 1578, and it's been there ever since.

Holes in the theory?
What about the biblical references to the risen Jesus conversing with the apostles, or eating fish to prove he was really real, or letting St. Thomas touch his wounds? De Wesselow noted that the first accounts of the crucifixion and resurrection were written down decades after they supposedly occurred. "In that time, there's plenty of room for all the legends to be added to the story. ... These are stories written by sophisticated individuals later on to prove the point that there was a physical resurrection," he said.

Is there any evidence that dead bodies could actually produce the sort of vaporograph that de Wesselow is talking about? "We haven't got anything precisely similar," he acknowledged, "but I don't think that's surprising."

He pointed to a phenomenon known as the Jospice Imprint: In 1981, a cancer patient died at an English hospice and left a partial imprint of his body and face on a mattress cover. "It seems to have been formed from urine pooling around his body," de Wesselow said. That's not what he thinks happened in Jesus' case, but he nevertheless cited the imprint as "another example of a strange image."

De Wesselow totally buys into the evidence provided by the Shroud of Turin Research Project, to the effect that the image is not an artistic forgery but the real imprint of a battered man from centuries ago. That's a huge leap of faith right there. If you accept that, there are only so many types of explanations for the shroud you can come up with. De Wesselow said his explanation addresses the shroud mystery as well as the roots of belief in Jesus' resurrection.

"There are explanations involving a miracle, or that Jesus was spiritually resurrected and appeared in visions to his disciples," de Wesselow told me. "Since the 18th century, scientists have tried to explain the resurrection, and they've basically given up. They've basically forgotten about the whole problem. What I think I can do is provide a fairly coherent explanation which is completely naturalistic. It's a better alternative to the traditional Christian view."

A skeptic speaks
Nickell, however, prefers to stick with his own skeptical view. "I think the resurrection appearances can be seen as pretty much the same kind of thing we have today with apparitional experiences — ghosts, if you will," Nickell said. "We could see ourselves in such a situation with, say, Elvis sightings. You can understand them as experiences that people had but were illusory."

The way Nickell sees it, the biggest argument against de Wesselow's "cloth-as-Jesus" hypothesis comes from the scriptures themselves: There are only vague references to burial cloths in Matthew, Mark and Luke. The gospel of John, meanwhile, refers to Jesus being covered by separate cloths for the face and the body, which is "fatal to the Shroud of Turin," Nickell said.

"The bottom line for me is, if this author were correct, and Jesus' shroud had survived, surely one of the holy evangelists would have made note of it," Nickell said. "If it had been kept and had a remarkable picture of Jesus on it, we would have known about it. And we don't."

So what do you think? Is the shroud a fake, a miracle, or the real relic of a dead man? Register your opinion by clicking on the poll above, and/or leaving a comment below.

More on the Shroud of Turin:

• Was Holy Shroud created in a flash?
• Documentary looks at the face in the Shroud
• 'Jesus-era' cloth casts doubt on Turin Shroud 
• Could new test settle Shroud of Turin debate?

Alan Boyle is msnbc.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

Antonio Calanni / AP file

The Shroud of Turin bears the faded image of what appears to be a Christlike figure. Italian researchers say they've come close to the shroud's coloration by blasting strips of linen with ultraviolet laser light.

Last updated noon ET Dec. 27:

Italian researchers have resurrected the idea that the Shroud of Turin's mysterious image of a Christlike figure could only have been created by a powerful flash of light — but skeptics still aren't buying it.

Scientists have tussled with believers, and with each other, over the origins of the centuries-old cloth for decades: Many believers think it's the true image of Jesus, left behind miraculously on his burial cloths after his resurrection. Analyses of the Shroud's chemical makeup, as well as radiocarbon dating of fiber samples, have led lots of researchers to conclude that the image was painted onto the cloth during the 14th century. But other researchers, sympathetic to the Shroud's cause, say those tests were faulty.

The Italian studies, conducted at the ENEA Research Center in Frascati, addresses a specific question in Shroud science: Could a burst of radiation have created the coloration seen on the linen? The answer is yes, although the results reported in the latest studies aren't a perfect match. So does that mean the Shroud image could only have been created by the flash of a miraculous resurrection? The answer is no, despite what you might read on the Web.

Five years of tests
"Sadly, we have seen many claims spread in the Web made by journalist/bloggers that discuss the content of a paper they never read," lead researcher Paolo Di Lazzaro told me today in an email. "It is obvious that a serious scientific work cannot prove any supernatural action. We have shown that the most advanced technology available today is unable to replicate all the characteristics of the Shroud image. As a consequence, we may argue it appears unlikely a forger may have done this image with technologies available in the Middle Ages or earlier. The probability the Shroud is a medieval fake is really low. In this sense, the Shroud image is still a scientific challenge."

Di Lazzaro and his colleagues based their conclusions on five years of tests, using an ultraviolet laser apparatus and strips of modern-day linen. They blasted the cloth with UV at different power levels, and reported that they "achieved a very superficial Shroud-like coloration of linen yarns in a narrow range of irradiation parameters." The best effect depended on laser pulses lasting less than 50 nanoseconds.

"These processes may have played a role in the generation of the body image on the Shroud of Turin," the researchers report.

They don't go so far as to claim a miracle. But the fact that UV laser blasters didn't exist in the 13th century, let alone in Jesus' day, strongly implies that they suspect something out of the ordinary was going on.

Di Lazzaro told me that the tests were not financed by ENEA, which is a government-sponsored research agency, and were conducted outside working hours. "The research was curiosity-driven, the attempt to replicate an image which is considered 'the impossible image' due to its very peculiar characteristics," he said.

Over the years, Di Lazzaro and his colleagues have published a long list of studies, including peer-reviewed papers (see below). The latest studies were presented at a May conference in Frascati and published in November as an ENEA technical report (with a disclaimer saying that the contents didn't necessarily express ENEA's opinion). But they didn't really get traction until this week, just in time for Christmas, thanks to a series of sensationalized British news reports.

Critiquing Shroud science
Shroud science, also known as sindology, usually percolates outside the scientific mainstream — but every once in a while a sensational claim comes into the public spotlight. Joe Nickell, an investigator for the New York-based Center for Inquiry, has been following sindology for decades. He noted that the Italian research revives a discussion going back to the 1980s, spearheaded by a group called the Shroud of Turin Research Project, or STURP.

"This is really nothing new," Nickell told me today. "This is a supposed vindication of STURP."

Nickell said Di Lazzaro and his colleagues started out with the assumption that the coloration on the Shroud couldn't have been created by applying pigment to the linen — which runs counter to the conclusions drawn by other studies. Starting out with the idea that the human figure shown on the Shroud is an "impossible image" stacks the deck in favor of a miraculous explanation, he said.

"Making the assumption of a miracle is a really, really, really, really, really big assumption," Nickell said. "That it's done in the name of science is just astonishing."

Nickell said the latest findings don't prove much of anything, even though they're dressed up in high-tech tests.

"It is made up of whole cloth," he said. "The pro-Shroud people start with the answer, and then they have to get some scientific evidence to back this up."

Some folks would suggest that the Shroud of Turin is a valuable focus for faith, whether it's real or not. What do you think? How much value is there in studying the Shroud, and how much impact do scientifico-religious debates like this one have on your own thinking? Check out the Web links below, give it some thought, and add your comments.

Update for 4:15 p.m. ET Dec. 22: Di Lazzaro sent a follow-up email calling attention to his group's publications, which I've added below, and he poses this question for Joe Nickell: "Was he (or anybody else) able to reproduce by chemical paint, acid and any other color a depth of coloration which is 0.2 micrometer thick (that is, one-fifth of a thousandth of a millimeter)? We are talking of this, because on the Shroud, the image has a coloration depth so thin that it is impossible to do with any kind of painting. I can quote peer-reviewed papers that show this is the coloration depth of the Shroud image.

"By the way, Nickell will be interested to know that using VUV photons we obtained this shallow coloration thickness," Di Lazzaro wrote.

I'll pass the question along to Nickell, who says he doesn't use email. I suspect the answer could go along two tracks: One is that it's a tough thing to try to reproduce a precise coloration depth under any circumstances. The other is that centuries of wear and tear might have had an effect that's not easily replicated by the contemporary application of pigments or other chemicals. But we'll see what Nickell has to say.

Update for 2:15 p.m. ET Dec. 23: Nickell responded to Di Lazzaro's question, and added a couple of questions of his own:

"Paolo Di Lazzaro claims the Turin 'Shroud' coloration depth is 0.2 micrometers, but surely he does not claim that that was uniformly measured throughout the cloth. The coloration indeed appears to be generally confined to the topmost fibrils (although the face image does show faintly on the back of the cloth). Using a two-part hypothesis I put forward in 1983, Italian chemist Luigi Garlaschelli has produced a replica shroud with such superficial staining. So let me ask Lazzaro a question in turn: Have you been able, using your high-intensity ultraviolet laser technique, to produce a replica shroud yourself? Until you do, shouldn’t you stop slashing carelessly with Occam’s razor?"

Here's a 2009 Reuters report about the Garlaschelli replica.

Update for 3:50 p.m. ET Dec. 26: Di Lazzaro sent this response to Nickell's questions via email:

"In 1978, several sticky tapes were used to sample the Shroud in different points of the body image. When the image fibers were pulled out of the adhesive, their colored coatings had been stripped off the fiber and remained in the adhesive. These coatings were independently analyzed by Profs. Alan Adler and Ray Rogers, and all of them were too thin to measure accurately with a standard optical microscope. This means the thickness of all coatings was smaller than the visible light wavelength, say thinner than 0.6 micrometer.

"Recently, these results have been confirmed by a direct measurement of another fiber, showing the thickness of the colored coating around the fiber is about 0.2 micrometer. As a consequence, there is quite a good probability most of the image fibers throughout the body image have a coloration depth smaller than 0.6 micrometers.

"Prof. Garlaschelli claimed he obtained 'a superficial coloration' without mentioning 'how much' superficial. Is it 100 micrometers thick? 10 micrometers? One micrometer? Nobody knows. I asked chemists [who are] colleagues at ENEA, and they told me it is impossible to obtain a coloration depth smaller than 10 to 20 micrometers with the chemicals used by Prof. Garlaschelli. This fact alone means the results of Garlaschelli are not comparable with the Shroud image.  Mr. Nickell may be interested to know Prof. Garlaschelli refused to reply the letter sent to the editor of JIST (the journal that published his results) where several points of his work were criticized, including the lack of a measurement of the coloration depth.

"Coming to the question of Mr. Nickell: We never claimed to have reproduced the whole Shroud image. We were interested to gain a deeper insight into the physical and chemical processes that generated such an unusual image. And we were successful to find photochemistry processes that are able to generate a Shroud-like coloration of linen fibers.

"Concerning Occam's razor, I am a scientist, and when I wish to understand a phenomenon, seeking for a scientific explanation, I use microscopes, spectrometers, image detectors and other laboratory tools. I see Mr. Nickell prefers using philosophical instruments like the medieval Occam's razor, a theory proposed in the 14th century. Each of us is free to choose the most familiar tool to find answers."

Update for noon ET Dec. 27: And Nickell responds...

"Di Lazzaro equates the depth of colored coatings that were stripped from surface fibers (using adhesive tape) with the depth of penetration that might be determined by cross-sectioning of actual threads, then asserts that a single fiber’s examination (still apparently not cross-sectioned) has 'confirmed' the dubious claims. Given the tremendous evidence against the 'shroud' — its incompatibility with Jewish burial practices, lack of historical record, bishop's report of the forger’s confession, the still-bright-red 'blood' which failed forensic serological tests, the presence of pigments and paints throughout the image, three laboratories' radiocarbon dating of the cloth to the time of the confession (1260–1390), and much additional evidence — it would seem that Di Lazzaro is straining at a gnat and attempting to swallow a camel. Let him produce a shroudlike image according to whatever theory he can muster, and we'll talk again."

The chatter on the Shroud:

• ENEA: Shroud-like coloration of linen fabrics by vacuum UV radiation
• Int'l Workshop on the Scientific Approach to Acheiropoietos Images
• Telegraph: Study claims Shroud is Christ's authentic burial robe
• Daily Mail: The Turin Shroud DOES have miraculous powers
• The Independent: Scientists say Shroud is supernatural
• Center for Inquiry: Turin 'Shroud' called 'supernatural'
• Telegraph: The Turin Shroud is fake. Get over it

Earlier tales of the Shroud of Turin:

• Documentary looks at the face in the Shroud
• 'Jesus-era' cloth casts doubt on Turin Shroud 
• Could new test settle Shroud of Turin debate?
• Public gets a look at the Shroud of Turin

Journal references from Paolo Di Lazzaro:

Peer reviewed Journals:
G. Baldacchini, P. Di Lazzaro, D. Murra, G. Fanti: “Coloring linens with excimer lasers to simulate the body image of the Turin Shroud” Applied Optics vol. 47, 1278-1283 (2008).

P. Di Lazzaro, D. Murra, A. Santoni, G. Fanti, E. Nichelatti, G. Baldacchini: “Deep Ultraviolet radiation simulates the Turin Shroud image” Journal of Imaging Science and Technology vol. 54, 040302-(6) (2010).

Conference Proceedings
P. Di Lazzaro, G. Baldacchini, G. Fanti, D. Murra, E. Nichelatti, A. Santoni: “A physical hypothesis on the origin of the body image embedded into the Turin Shroud” Proceedings of the Int. Conf. on The Shroud of Turin: Perspectives on a Multifaceted Enigma, edited by G. Fanti (Edizioni Libreria Progetto Padova 2009) pp. 116 – 125. ISBN 978-88-96477-03-08 01-12.

P. Di Lazzaro, G. Baldacchini, G. Fanti, D. Murra, A. Santoni: “Colouring fabrics with excimer lasers to simulate encoded images: the case of the Shroud of Turin”, XVIII Int. Symposium on Gas Flow, Chemical Lasers, High-Power Lasers, edited by R. Vilar, Proceedings SPIE vol. 7131 (2009) pp. 71311R-1 – 71311R-6.

P. Di Lazzaro, D. Murra, A. Santoni, G.- Baldacchini: “Sub-micrometer coloration depth of linens by vacuum ultraviolet radiation”, Proc. International Workshop on the Scientific approach to the Acheiropoietos Images, edited by P. Di Lazzaro (2010) pp. 3 – 10.

D. Murra, P. Di Lazzaro: “Sight and brain, an introduction to the visually misleading images”, Proc. International Workshop on the Scientific approach to the Acheiropoietos Images, edited by P. Di Lazzaro (2010) pp. 31 – 34.

Technical Reports
G. Baldacchini, P. Di Lazzaro, D. Murra, G. Fanti: “Colorazione di tessuti di lino con laser ad eccimeri e confronto con l’immagine sindonica” ENEA RT/2006/70/FIM (2006).

P. Di Lazzaro: “Wissenschaftliche Hypothesen zur Entstehung des Bildes auf dem Turiner Grabtuch” 30Tagen n.4 (2010) pp. 63-66.

P. Di Lazzaro, D. Murra, E. Nichelatti, A. Santoni, G. Baldacchini: “Colorazione similsindonica di tessuti di lino tramite radiazione nel lontano ultravioletto: riassunto dei risultati ottenuti presso il Centro ENEA di Frascati negli anni 2005 -2010” RT/2011/14/ENEA (2011).

Alan Boyle is msnbc.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.