What we think we know for sure about the Shroud—Just isn’t so. For instance, consider this careless statement from the Sign From God Foundation:

Fact: The mysterious image is the result of dehydration and oxidation of the cellulose fibers composing the linen. There is no known artistic process used in the Middle Ages that could account for the image.

Not good. That’s not a fact. It’s a disputed observation and an impossible negative hypothesis wrapped in theological marketing. It falls apart under scrutiny.

We might begin with the quip popularized by The Big Short:

It ain’t what you don’t know that gets you into trouble. It’s what you know for sure that just ain’t so.

Wrongly attributed to Mark Twain, these words capture something deeply relevant about the way claims about the Shroud are made. The Sign From God Foundation’s statement exemplifies the danger of clinging to apparent certainties in the face of conflicting, evolving, and often contradictory evidence.

 The Chemistry of the Image: A Web of Contradictions

The claim that the image was formed by oxidation and dehydration of cellulose microfibrils stems from the 1981 STURP (Shroud of Turin Research Project) report. It sounded authoritative at the time. But scientific understanding has shifted, and with it, confidence has eroded.

From the outset, John Jackson, who headed up STURP, has maintained the position that no pigments or paint-carrying media were found. He has suggested a direct chemical alteration of the linen fibers themselves, with no external materials responsible for the coloration. This conclusion, if true, might appear to push the image into the realm of mystery. However, it does not close the debate. It opens it wider.

Ray Rogers, STURP’s own lead chemist, instead, suggested a Maillard reaction, resulting from gaseous amines interacting with a starch-based contamination layer on the Shroud. He found evidence of this contamination. Others, like Heller and Adler, did not. These aren’t quibbles; there are significant scientific disagreements at the foundational level of what the image even is chemically.

Colin Berry, a British chemist and a modern critic of Shroud authenticity, rejects both Jackson’s and Rogers’ conclusions. He contends that Rogers mischaracterized the surface chemistry of linen and that the image was the result of contact scorching or some medieval image-transfer process. Berry’s experimental replications, though not perfect, serve the purpose of showing that image formation by natural or artistic means cannot be ruled out.

When scientists of this caliber—Rogers, Jackson, Berry—propose fundamentally different explanations, the only legitimate conclusion is reasonable doubt.

The Sign From God Foundation’s rhetoric relies on the phrase “no known artistic process.” This is not science; it’s courtroom-style persuasion. In a criminal trial, “proof beyond a reasonable doubt” is a powerful standard—it means that no other explanation makes sense. But for scientific inquiry, this is always premature and irresponsible when the evidence is still disputed.

Scientific inquiry isn’t about winning a case; it’s about converging on truth through consensus and replicable results. If, 45 years after STURP, there is still no agreement on what caused the image, then we’re not at the “reasonable doubt” threshold. We’re in the middle of a scientific controversy that demands further research.

Cherry-Picked Consensus Is Not Consensus

The claim that “there is no known artistic process used in the Middle Ages that could account for the image” is contradicted by practical demonstrations.

Joe Nickell, using bas-relief techniques, and Luigi Garlaschelli, with his 2009 UV photo-negative replication, both demonstrated how plausible medieval methods could account for the Shroud’s general appearance—including superficiality and negative imaging. While not identical to the Shroud’s image, these efforts are more than enough to undermine the absolute certainty that the Sign From God Foundation tries to project.

There is also Walter McCrone, whose microscopic work suggested the image was painted using iron oxide pigment. Though later disputed, his findings remain part of the body of evidence that keeps the image’s origin an open question.

Some may argue that McCrone’s findings raise considerable reasonable doubt. While his conclusions have been challenged by other researchers, they are still cited by skeptics of the Shroud’s authenticity. For a well-articulated and scientifically rigorous defense of McCrone’s position, see Joel Bernstein’s lecture, Good Science, Bad Science, and the Shroud of Turin, available on YouTube. Bernstein, Global Distinguished Professor of Chemistry at NYU Abu Dhabi and former Barry and Carol Kaye Professor of Applied Science at Ben-Gurion University, offers a compelling critique of theories that dismiss pigment-based explanations without sufficient justification.

From Evidence to Faith: A Problem of Category

The Sign From God Foundation crosses a line when it packages open scientific debate into a tidy conclusion to support evangelization. Their assertion that the image must be miraculous because “science can’t explain it” is a textbook case of the God of the gaps—a retreat from mystery into dogma.

To quote science writer Philip Ball:

There’s no shortage of hypotheses. Some suggest that the image came about through natural processes; some impute considerable ingenuity to medieval forgers of relics; others invoke wondrous physical processes associated with the Resurrection. But do any have any merit?
(BBC News, 2015)

The answer is: some do, and some don’t—but none are conclusive. And that’s the point. When evidence is controversial and explanations conflict, scientific integrity demands openness, not theological certainty disguised as objectivity.

Reasonable Doubt as the Proper Scientific Response

A detailed 2010 paper from the Shroud Science Group tried to classify Shroud observations into “Type A: unquestionable facts” and “Type B: confirmed observations.” But even their most confident claims—like “the color resides in the primary cell wall”—are couched in tentative language: “probably,” “seems,” “likely.”

This isn’t weakness; it’s the strength of honest science. But it also reinforces that we are not at a point where we can assert a definitive mechanism for image formation, nor rule out artistic or naturalistic origins.

Even Hugh Farey, an open-minded skeptic, put it well:

De-controversialisation, if such a word there be, is the goal of all scientific investigation… The best representation of truth that he can come up with, in such a way that there is no longer any controversy about it, is every scientist’s dream.

We are not there yet.

Call It What It Is—Mystery, Not Fact

What the Sign From God Foundation presents as “fact” is not only disputed—it’s deeply entangled in decades of conflicting interpretations, failed replications, and contradictory results. It is not “proof beyond a reasonable doubt.” It is, at best, a hypothesis still awaiting resolution.

Until the science is de-controversialized, the Shroud should not be used as a tool for evangelism or apologetics. To do so is to turn scientific uncertainty into a spiritual sales pitch—and that, more than anything, should give us pause.

One More Thing As Illustration

The case of Walter McCrone illustrates, in a particularly striking way, how scientific disagreement, when not responsibly resolved, contributes to the enduring uncertainty that surrounds the Shroud of Turin.

McCrone, a respected microscopist known for identifying forgeries like the Vinland Map, examined sticky tape samples taken from the Shroud in 1978 and concluded that the image had been created using iron oxide pigment—specifically, red ochre and vermilion. He saw what he believed were clear indicators of artistic application, suggesting the image had been painted, albeit dryly, onto the cloth by a medieval forger.

Members of STURP—the research team that had initially been provided the samples—strongly rejected this. Their chemical analyses, led by John Heller and Alan Adler, found no evidence of paint binders or media, no brush strokes, and no signs of pigment distribution consistent with painting. Ray Rogers, the chemist who had supplied McCrone with the tapes, later stated that McCrone had misinterpreted environmental contaminants—naturally occurring iron oxide particles—as evidence of artistry.

And so, McCrone’s view was dismissed. Not entirely discredited in a scientific sense—his data were never shown to be fraudulent—but effectively excluded from further collaboration. The disagreement became adversarial, not constructive. To my knowledge, there was no sincere, prolonged attempt to resolve the differing interpretations, no joint publications, no shared experiments. The argument played out in journals, press statements, and public commentary. McCrone was on one side; STURP was on the other. The image chemistry remained, and still remains, an unsettled matter.

This wasn’t just a missed opportunity for collegiality. It was a scientific failure.

If McCrone was wrong, as many believe, then engaging his methods more directly—replicating his tests, reviewing his microscopy under more advanced imaging, revisiting his samples—might have clarified the matter beyond doubt. If he was right, or even partially right, then we might now have a more honest account of how the image formed. Either way, the failure to resolve competing hypotheses has left us with unfinished business—an image still unexplained, forty-five years later.

And let’s be honest: the McCrone affair is not an isolated case but part of a broader pattern. Disagreements about whether the image resides in the cellulose, in a starch layer, or in some ghost-like coating still persist. There is no shared conclusion, no accepted chemical profile. And while new hypotheses are floated—radiation, Maillard reactions, scorching, vapor diffusion—the foundational questions remain unsettled. No one has de-controversialized the chromophore, as Hugh Farey might put it.

This is not how science is supposed to work. Contradictory evidence is supposed to lead to more research, not more rhetoric. And the longer we allow speculation, tribalism, and theological agendas to dictate the conversation, the further we drift from meaningful understanding.

So, if the Sign From God Foundation wants to call something a “fact,” let it be this: the chemistry of the image on the Shroud of Turin has not been resolved, and the reason is not that we lack evidence—it’s that we’ve failed, again and again, to fully follow the evidence where it leads.