Modelling the Turin Shroud: forged in the 14th century as a white flour imprint onto linen? Then chemically developed with nitric acid to resemble ancient yellowed sweat?

What follows is a concise summary of several weeks of somewhat hazardous research, first with sulphuric acid, then nitric acid, in the author’s garage. The numerous experiments that led up to it, with minute to minute photography and interpretation, are all described on his sciencebuzz site, this site having been mothballed some months ago and now reactivated. I have decided against placing images on this posting – they can all be found on sciencebuzz.

Note: the author is a retired biomedical scientist, best known for his research into cereal dietary fibre and resistant starch. His aim is NOT to produce a facsimile copy of the Turin Shroud (not having access to it, even simply to examine through a hand lens would make that difficult). It is merely to suggest how  it might have been produced, as a riposte to those misguided souls who would have us believe that the so-called ‘enigmatic’ features of the TS image – negative superficial image, 3D properties etc. – place it beyond the realms of conventional science, “not made by human hand”, a product of supernatural radiation etc etc.

As I say, this is just a bald summary, with no attempt at literary flourishes.

1. The so-called Shroud of Turin  was probably made in the first half of 14th century, in agreement with the radiocarbon dating. (I say “so-called” because I don’t consider it was made to represent a burial shroud at all – see below).

2. It built on the idea of the Veil of Veronica, the latter having according to legend having captured a likeness of the face of Jesus imprinted shortly before crucifixion onto a face cloth. The Veronica was then Christianity’s most venerated relic, despite it having no biblical authority. In contrast, the new cloth, the new ‘relic’, WOULD have biblical authority. What’s more it would show the entire body of Jesus, front and back.

3. The three synoptic Gospels provided a legitimizing ‘window of opportunity’ for creating a whole body image on cloth before consignment of the crucified Jesus to the rock tomb. All make clear that Joseph of Arimathea’s sheet of linen was used to receive the body at the cross itself (not the tomb) for discreet and dignified onward transport to a nearby tomb. In other words the cloth functioned not only as an impromptu stretcher but, in the instant visual narrative created by the TS, as an up-and-over ‘body bag’ too, given its length (approx. 4.4 x 1.1 metres). There are no strong grounds for thinking J of A’s linen was intended as the final burial shroud. The account in John suggests otherwise, it being replaced by Nicodemus’s “winding” sheet.

4. The new image was therefore to be that of the crucified Jesus on J of A’s linen. It would have the bloodstains obviously. But how to represent the body? Answer: by supposing that the body left a sweat imprint too, one that had yellowed or browned over 13 centuries.

5. The imperative was to produce an image that would be interpreted immediately by relic-hungry pilgrims as an IMPRINT, not a painted image. How was that ensured? Answer: first by showing a LIFE-SIZE image of a naked man (clothing, even a loin cloth would interfere with imprinting of sweat). Second by showing both frontal and dorsal surfaces aligned head to head, with a small gap between the heads, so as to be suggestive of an imprint formed on an up-and-over sheet of linen. Third, it would be fine linen (herring bone twill) consistent with the biblical account. It is the fourth detail that is the crucial one: the image would not be that as in an artist’s portrait, with light and shade used to give the appearance of form, depending on direction of light, with prominent features like nose, chin and forehead appearing light, and recessed features like eye hollows being dark. Everything would be reversed. Raised relief would be dark, recesses would be light, because that is the reversed pattern that one sees after IMPRINTING BY CONTACT, as distinct from portrait painting, or modern photography. However, we can describe the desired outcome as saying it was to resemble a photographic negative, centuries before photography was invented.

6. No attempt would be made to imprint images of wound sites (from flagrum, nails, lance) – too difficult. Instead blood (or blood substitute) would be applied in all the biblically correct places at the sites of those wounds.

7. The body image would have to be imprinted first, so as to know where to apply the blood.

8. The task then becomes one of creating a NEGATIVE imprint off both sides of a naked man that would be yellow or yellowish-brown in colour for body, with additional bloodstains. It needed to be clearly visible, viewed at close quarters, say a few metres, but not too prominent.

9. A painted image was ruled out. First, it is difficult to paint by freehand a convincing negative image intended to be seen as an imprint. Second, paint pigments would be immediately recognized as such. A more subtle means or mimicking an ancient dried-on sweat imprint needed to be found, using novel one-off technology if necessary.

10.  Novel one-off technology might indeed have been deployed and available in the 14th century (possibly with the aid of alchemy).  The first of two steps required choosing an organic-based material that could used for imprinting the negative image that could then be made, in a second step, to turn yellow, or yellowish brown, by treatment with a “developing” agent. In other words, the image was to be produced not by photography, but a tactile equivalent (contact imprinting) followed by chemical development. The TS image might thus be described as a TACTILE CHEMOGRAPH.

11. It was reasonable to suppose that acids would be considered as chemical development agents, not the weak acids of nature (acetic, lactic, citric etc ) but the far stronger MINERAL ACIDS. The three most important, found in all chemical laboratories, are: hydrochloric (HCl), sulphuric(H2SO4) and nitric (HNO3). Descriptions, and methods of making these three all began to appear in the 13th/14th century alchemical literature. Which would be seen as prime candidate for developing an organic imprint to simulate sweat? Answer: nitric acid. Why? Because inadvertent splashes of nitric acid onto skin quickly become bright yellow or orange. It’s an example of the so-called xanthoproteic reaction, used in fact as a quick test for protein. At first sight a nitric acid stain on skin might seem to be a “burn”, but it’s not. It’s far more subtle. The nitric acid is reacting with certain amino acids in skin protein (keratin) specifically  the so-called aromatic amino acids, producing yellow or orange-red  nitration products. The prime target is generally considered to be the amino acid tyrosine, being phenolic and thus chemically reactive towards nitro-substitution. One or two others (tryptophan, phenylalanine) may or may be targets as well (the literature is confusing). One report claims that tyrosine and tryptophan give different colours (yellow and orange respectively) which may or may not be relevant to the TS “sepia” image.

12. 13th/14th century alchemists knew nothing about the mechanism of the xanthoproteic acid, only the end result – that certain organic materials turned yellow or orange when treated with nitric acid. Which organic material would have been chosen for imprinting. It would have to be one that could be smeared or painted onto a human subject (living or dead) to which blood spots and trails could then be added, and the two ingredients then efficiently transferred to linen by imprinting, ready for the second stage development with nitric acid.

13. White flour from wheat fits the bill, as least in principle. A cold dispersion in water, i.e. paste or slurry, acts as a fairly fast (but not too fast) adhesive, helping stick things together, like the photos in a home-made album this author made as a young child. Flour slurry, of the right consistency, allows linen to mould itself closely to body contours,. When one removes the linen, the adhesive properties of the rapidly drying paste are apparent. Flour transfers efficiently to linen, leaving the skin stripped almost clean of flour.

14. (Late addition in italics – in response to first comment below; original version shown scored through).  After ‘painting’ the human subject with imprinting medium (flour paste etc), blood is added in trickles directly on top of the paste in all the biblically correct places (before the latter has time to dry). Subject and linen are then brought together under some pressure to get a conjoint imprint of medium and blood. When the linen is peeled away, one has blood imprint UNDER body image, thus modelling the Heller/Adler finding from protease digestion, i.e. that there is no body image under the bloodstains.

The negative flour image can then be dried, blood, or blood substitute added, and then  The imprinted linen is then either (a) exposed to the vapour from concentrated nitric acid or (b) steeped in nitric acid solution of approx 10% w/v concentration or greater. The yellow-brown image takes several hours to develop in vapour, usually with faint discoloration of the linen per se. Image development is much faster in solution (typically an hour or less) but the linen is more discoloured.

15. The colour is due to reaction between the nitric acid and flour protein, notably the viscoelastic gluten, so crucial for breadmaking. Starch contributes at most a trace of faint yellow colour. That is easily demonstrated by making a stiff dough of white flour with water, then kneading it under water. The starch granules wash out;,  leaving a much smaller ball of rubbery gluten. One then allows the starch to sediment under gravity, such that it and gluten can be tested side-by-side with nitric acid. The gluten turns orange, the starch is scarcely altered at all.

16. To conclude, a new model has been described for how the TS body image was produced as a medieval fake/forgery/hoax, one that could be promoted as representing the sweat (and blood) imprint left by the newly crucified Jesus on Joseph of Arimathea’s linen.

The model still needs a name, more or less specific for the unique chemistry proposed, based on nitration of food proteins (admittedly a leap of faith there, inasmuch as other combinations of imprinting medium and chemical might result in a developed sepia image).  But my gut instinct says it’s nitric acid and food protein.  So why not call it the xanthoproteic model? That means – yellow/protein in plain English.

Comments on the science and technology are welcome, but this is not the place for discussing theological implications. Theology may occasionally benefit from an input of science, to be carefully distinguished from pseudoscience, but – with no disrespect to Stephen Hawking- science rarely if ever benefits from an input of theology.

PS: please ignore the banner on this blog (due to be replaced).  It was designed to convey the essence of the model that preceded the one set out here – i.e. the contact scorch model. It seemed to have quite a lot going for it, a scorched-on image being symbolic of the way that an alleged Templar uncle of the Shroud’s first known owner (Geoffroi de Charny) had been executed by sadistic slow-roasting alongside Jacques de Molay in 1314.  So what prompted the flight from thermal imprinting to wet imprinting/chemical development? It was little or nothing to do with the properties of thermal scorches, vis-a vis the TS. The latter has often been described as “scorch-like”.  STURP almost said as much in its 1981 Summary.  No, it was one tiny detail on the Machy mould for a second Lirey pilgrim’s badge – a small inset image on the border of what clearly was the face of Jesus above the word SUAIRE.  I (and possibly I alone) took that to be an allusion to the Veil of Veronica face cloth. Whether it was or not hardly matters – it was the realization that a simulated sweat imprint ticked a lot more boxes than a heat scorch, provided some of the drawbacks of wet-imprinting could be solved, e.g. reverse side coloration, maybe via minor changes of technique. Both of course are imprints, so either can be a valid working model for exploring the generic properties of imprints – their negative character, 3D properties etc – as proved to be the case with the “wasted years” focused on thermal scorches. Much know how was acquired exploring linen properties and its ability to acquire a superficial image by different means.


About Colin Berry

Retired science bod, previous research interests: phototherapy of neonatal jaundice, membrane influences on microsomal UDP-glucuronyltransferase, defective bilirubin and xenobiotic conjugation and hepatic excretion, dietary fibre and resistant starch.
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4 Responses to Modelling the Turin Shroud: forged in the 14th century as a white flour imprint onto linen? Then chemically developed with nitric acid to resemble ancient yellowed sweat?

  1. Mark One says:

    Your research experimentation is fascinating and your blog is like a little island of near-sanity in a storm-tossed sea of hype (much of which is the result of the machinations of people with vested interests – not just religious groups, but also the press). I myself am an atheist, so I have no axe to grind other than wishing for an open-minded, scientific and empirical approach to the problem.

    You warn against mistrusting fellow scientists, and you may well be wise to do so, but your Point 7 (“The body image would have to be imprinted first, so as to know where to apply the blood”) flatly contradicts Heller and Adler, who are quoted as saying in the Canadian Society of Forensic Science Journal (1981) that the image colour does NOT appear under the bloodstains when the bloodstains are removed with a proteolytic enzyme. I take this to mean that the blood must have “coloured” the linen BEFORE the body image was created.

    Are you refuting Heller and Adler’s statement? If so, it would be interesting to know on what grounds. “Take nobody’s word for it” is a fine starting-point, but supposing they’re right?

  2. Colin Berry says:

    Ooops. Silly me. I already had the Heller/Adler requirement catered for in the two stage methodology proposed here, then went and clean forgot about it. So here’s the necessary amendment/correction, which I’ll insert shortly. The blood is added as dribbles directly on top of the flour paste BEFORE second stage imprinting. That way it imprints onto linen first, so ends up UNDER the body image, not on top, as would be the case if blood had been applied after imprinting. Must stop there: laptop playing up. Thanks for spotting and reporting the error.

    • Mark One says:

      Thanks for taking the trouble to field my query, and for providing a lucid explanation. As I understand it (as a non-scientist), the core of your idea is a two-stage process of image formation, analagous to pre-digital photography: (a) taking the photo; (b) developing it as a negative. The blood is added between the two stages.

      The blood, of course, is a bridge that will have to be crossed later. It’s interesting to note Adler’s comments about the blood (referenced in Kearse’s “Immunological Review”, 2012:

      I like the way you work. You are right to challenge suggestions of supernatural involvement by attempting to reproduce image formation in this manner. It always worries me when I hear someone say, as scientists, journalists and mystics often do: “THAT can’t possibly have happened”. If you succeed in developing a putative image-formation technique which could have been executed by anyone in the 13th/14th century, you will have disproved the “can’t possibly have happened” normative statement, which would be a significant step forward in TS research.

  3. Colin Berry says:

    Yes, image capture first, maybe scarcely visible, followed by a separate second stage to augment the visibility. It’s analogous to pre-digital photography, but as I was saying just the other day to someone on the shroudstory site, it’s possible that the two-stage process could have been in operation many centuries earlier, at least in principle. Imagine someone pressing their face down into a pillow. They leave an indentation, which is a kind of negative image of sorts, but it’s faint and it’s temporary (disappearing as soon as the pillow returns to its original shape). But suppose they had first smeared their face with oil, before pressing in into the pillow. It’s a faint imprint in oil, but it’s permanent, remaining visible after the pillow has sprung back.

    So far we’ve achieved Stage 1 imprinting. We now want to develop the image further. If oil had been used as imprinting medium, there’s a way of doing that. One finds something that attaches preferentially to oil rather than fabric. Thinking about the way fingerprints can be revealed by dusting. one could try blowing soot (fine particles of carbon) onto the oil imprint. There’s a good chance they would stick to the oil and resist being shaken off. One has then achieved second stage development.

    By the same reasoning the TS image could have been produced by 1. impaction of a flour/water paste coated human (+ blood) onto linen to leave a faint negative image. Then, Step 2, develop the image by exposing to a suitable chemical that forms a strong yellow colour with flour but not linen. Nitric acid, either as vapour or solution, fits the bill. I consider this technology to have been fully within the means of a medieval entrepreneur, especially one who had links with an alchemist and who knew the recipe for generating nitric acid (heat a mixture of Cyprus vitriol, alum and saltpetre).

    Thanks for your interest and appreciative comment, Mark One

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