Thibault’s Principle: true for a stepped template, maybe – but not an artistic bas relief with rounded contours and gentler relief


Try to avoid too many flat surfaces and  right angles when choosing a template for your Man in the Shroud 😉

Thibault’s Principle:  “No scorch produced by pressing a heated template onto linen can hope to match the subtlety of the Shroud image, either at the macroscopic or microscopic level.”

I suppose it should be called Heimburger’s Principle.  It’s Thibault Heimburger MD. But let’s keep this informal if we can.

In fact, he didn’t state it in those precise words, but it is implicit in everything he said, and probably what John Jackson said, whom he quotes. Here’s a flavour:

Thibault:  Page 6/24

(pdf document)

“In other words, even with a less than 1 millimeter high relief, either the relief has the right color and the neighboring areas have no color either the neighboring areas have the right color and the relief is much too colored.”

And as I say: Thibault then looks to John Jackson for support with this:

“This problem of contrast has already been discovered by Jackson.”

I have briefly discussed Jackson’s work on a previous occasion, and declared my admiration for what he achieved, whilst having reservations on a number of grounds. But it is not his work that is in the frame today, but Thibault’s.  Today I concentrate on the macroscopic aspects of the Thibault Principle (the microscopic ones will follow later),

They say a picture is worth a thousand words. Well, here’s a few pictures that convey why I think the Thibault Principle as enunciated above is irrelevant to the Shroud image, due to use of an inappropriate template that by no stretch of the imagination could be described as ‘bas-relief’ relevant to the human form. Yes, I’m all in favour of simplified models that hone down to essentials, eliminating as much superfluous detail as possible, but a flat chunk of metal that is virtually right angles and slots is simply not ‘fit-for-purpose’. Sorry to have to be so frank, Thibault, but “nul points” re your choice of template, and nul points to any and all conclusions based on that choice,

Note Thibault’s “contrast problem” with the first of his two templates with sunk relief. It is essentially due to an excess of facing plane over vertical plane, with excessive imprinting of the first encountered plane relative to the next-encountered sunken plane. (I may wish to revise that wording later).

Thibault also used a raised relief version, with a smaller height difference between planes (1mm) but the basic problem remains: too much frontal plane, and greater contact pressure with the first encountered plane relative to the second. Again, one expects a “contrast problem”.

use a proper bas relief template instead, with a much better mix of resolved vertical and horizontal planes, with smooth rather than stepped transition between the two, and one avoids that “contrast problem”. One gets a range of contrast values instead that depend on the angle of contact between metal and linen as well as the height difference between basal plane and each feature or prominence of interest.

Now this is what I call a proper template – a BAS-RELIEF – with a complex mix of vertical and horizontal planes, many of them neither completely one or the other, ie. the metal makes contact with linen at a whole range of angles between 0 and 90 degrees to the normal.

A good old English horse brass – a bas-relief.

And here is a pair of scorch marks from that same bas relief template. Contrast probem? I see no contrast problem. Why should there be a contrast problem? Demonstration of the Thibault Principle? I see no demonstration of the Thibault Principle.

More to come, but I hope folk will see that as far as the macroscopic level is concerned , Thibault’s Principle has failed to put in an appearance in my experiments, and would not have in his either if he had made a sensible and appropriate choice of template. Given that he cites Jackson’s work, and looks to him for support, then why did he not take a leaf from Jackson’s book and choose a proper BAS-RELIEF template?

The trickier party of responding to Thibault is yet to come, i.e. in addressing the comparison between the Shroud image and model scorches at the microscopic level. All I would say for the moment is that one is not comparing like with like, age-wise, and allowance must be made in one case for wear and tear. The Shroud image probably looked very different centuries ago – both to the unaided eye and under the microscope.

I shall now take a break for a day or two, while, as I say,  reserving the right to edit this somewhat hastily-assembled post…

Postscript: the crucial aspect re templates and imprinting is that subtle factor of frontal v. vertical plane of presentation. Imagine for a moment you had some linen spread over a sand bed, or some other underlay designed to get best contact between heated template and linen. (I’ve switched from using sand to a few layers of thick fabric). Imagine one had a small cube or sphere of soft metal that could be hammered into any shape one desired.

One could either have maximum area of initial contact, or minimum area of initial contact. If it were the first of those one would hammer out the metal to get a thin but rigid sheet, and then press it into the linen. But there would be a lot of resistance, and rather good imprinting (scorching) all over if the metal were hot. Suppose one presented it edge on – in other words the thin edge of the metal plate.  Then there is now something like a blade that allows one to get a lot of contact laterally in terms of area  (not on the leading edge, with its small area) but at a tangential angle, close to the parallel,  that will not be conducive to scorching EXCEPT for the tiny area of the leading edge.  Same amount of metal, but high contact pressure and all-over scorching in one instance, and low contact pressure (per unit area) and little scorching in the other (except for that intensely scorched leading edge).

In practice, any given object is somewhere intermediate between those two extremes.  Thibault’s template is at one extreme, with a lot of contact pressure, whereas a bas relief is intermediate. There is the added subtlety that Thibault’s template is a pair of planes, separated by a small shelf, and while the distance of vertical separation is small, a mere 1mm in his raised relief template, it is enough to give a large difference in contact pressure and scorching of the first plane making contact with the linen and the second. A bas relief on the other hand penetrates more deeply, with its greater proportion of vertical to frontal plane, and thus one sees less of that “contrast problem” on which he places  so much emphasis (excessive emphasis in my view).

Afterthought:  Wed 24 October  Re UNDERLAY

Early in my own studies I reported the importance of underlay for good thermal imprinting, alluded to briefly above. The crucial factor was to imprint vertically into the linen, the latter being spread initially over dry or dampish sand. Later I found a folded-up pad of thick floor cloth to be effective in getting good detailed imprints. It’s not difficult to see why – there has to be a resistance to “push” the linen up into the holllows and recesses of the bas relief to get maximal metal-linen contact, capturing as much detail.

But when you look closely at Thibault’s reports of each experiment, one gets the impression that he was slow to appreciate the importance of underlay, at least  initially. In his first experiment he seems to be pressing linen DOWN onto hot metal, presumably gripping it at the sides and ‘stretching it over’.  That would explain why the sunk relief portion in the centre was so poorly imaged. Later he talks about using a “firm surface”, suggesting that he had by then adopted my vertical presentation, using the template as one would a date-stamp, and later still there is a reference to a “soft pillow”.

I cannot stress too strongly the importance of underlay. Some of the “excessive contrast” that Thibault’s paper claims makes scorching a non-starter where medieval forgery is concerned can be explained simply by his failure to provide an underlay with the right combination of “give” and resistance, ensuring maximum contact between template and linen.

Update: Quote of the day from “Andy Weiss” on The Other Site:

October 24, 2012 at 11:07 pm | #20

“While that may be so, Yannick, my question remains unanswered. If my thoughts are accurate with reality, anyone asserting the image is a scorch is no scientist.”

Thank you Andy. You say such nice things…

Has it not dawned on you that there may be more to science than mere “thoughts”, assuming that is you wish to stay “accurate with reality”? Ever heard of experiments, hypothesis testing etc?

Colin Berry  (retired biomedical scientist)


This critique of TH’s dismissal of the Scorch Hypothesis continues on a more recent posting here on my own site:

Nul points. Thibault Heimburger etc



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.
This entry was posted in medieval forgery, Shroud of Turin and tagged , , , , , , , . Bookmark the permalink.

30 Responses to Thibault’s Principle: true for a stepped template, maybe – but not an artistic bas relief with rounded contours and gentler relief

  1. Hugh Farey says:

    A confusing day.

    I’ve been heating a) my faithful spatula, b) my faithful spoon, c) a china thingy, d) a metal pony (which actually melted after being heated too much) and have come to various conclusions, mostly contradictory.
    1) The best image results in terms of graduation of shade come from china. The heavy contact can be not too dark, the light contact not too light, and a bit of non-contact still visible. The trouble is that the discolouration seems to cover entire areas of threads, including the hidden surfaces and the back of the cloth.
    2) The best fibre results come from metal, but with a very brief contact time (a second or less). Only the very tops of the fibres are scorched and the resemblance to Mark Evans’s photos is marked. However, you have to be very quick to get variation of pressure, and I never achieved it. Either the hard contact was burnt through, or only that area was visible at all.
    3) From a photo processing point of view, a negative of almost any of these experiments looks amazing. Rather than being astonishing, I’m beginning to think that the most remarkable aspect of the shroud is in fact rather commonplace.
    4) My bas-relief effect (on Adobe Elements) is pretty primitive, so I can’t really say anything about the 3D (VP-8 Image Analyser) effect.
    5) All attempts not to get fluorescence, and to remove it, have failed completely.
    6) I read somewhere that pink fluorescence might be due to the charring of the cloth in the absence of oxygen. I tried heating a bit of linen tightly wrapped in tinfoil, and also inserting it into a test tube with boiling water in the bottom (driving out the air). Fluorescence remains firmly greeny yellow.

    Next steps:
    a) Buy a bit of brass… (my pony looking a bit warped now)
    b) Try to remove the upper layer of marking with a piece of sellotape
    c) Try to prep the cloth with a mixture of starch, sugars and saponin – soapy custard in fact – to see if I can get an extra layer on the surface of each fibre.

  2. colinsberry says:

    Brilliant observations Hugh. Too much to respond to you point by point right now, but I shall endeavour to do so in the fullness of time…

  3. Matthias says:

    Re: Hugh’s no. 5 – so you couldn’t avoid fluorescence. Is this not a problem for the scorch theory, given that the Shroud image, from what I understand, does not fluoresce under UV?
    Sorry, unlike you both I am not a scientist, so you will have to excuse my scientific limits!

  4. Hugh Farey says:

    Thanks, Matthias; it is certainly a problem, and is the first and most obvious reason for people to say “the image cannot be a scorch.” However, it raises a lot of quite testable corollaries.
    1) Can the UV fluorescence be somehow removed?
    I’m working on that.
    2) Does it fade with time? (Not since the burn-holes – 500 years, but since Christ – 2000 years?)
    Not easy to experiment with, but has anybody tested other old scorches, from
    archaeological finds dating from the 1st to 14th centuries?
    3) Can we achieve a scorch-like mark (with low temperatures, light, nuclear radiation, chemicals, magic…) which does not fluoresce in the first place?
    I’m working on that too.
    4) Can we duplicate the pink fluorescence of the burn-holes?
    And that.

    If, after trying dozens of things, I can’t either remove or prevent the fluorescence, I still cannot be certain that it isn’t possible, but it does shift the weight of evidence. As it stands, however, I am not aware that anybody has carried out these tests at all.

    • Matthias says:

      Thanks Hugh, will be interested hearing further of your experiments.
      Re: 2 – we would only need to think of of 700 odd years with regard to medieval forgery hypothesis. If we could prove that burns 700 years of age can not lose fluorescence, then that would go some way to dispelling the medieval forgery by scorch hypothesis. In that respect, is not Adrie’s comment below pertinent in terms of scorches from presumably the 1500s coming up with green fluorescence have not lost their fluorescence with time (some 500 years of it)

      • colinsberry says:

        Good day to you Matthias

        Who knows – maybe fluorescence will be the downfall of the medieval forgery hypothesis. But if it is, I hope that it won’t be based purely on the presence or absence of green or any other fluorescence. That is not science. That is witchcraft – unless, that is, one knows precisely which pyrolysis product(s) is responsible for that fluorescence and can develop a detailed physical and chemical rationale. Oh, and let’s not forget that a fluorochrome can be present, but fail to fluoresce under uv due to the presence of one of more quenching agents. One of the commonest quenchers is ordinary ground state (triplet) molecular oxygen. All it takes to quench quinine’s blue fluorescence is some chloride ion.

        There’s another reason for not being too hasty in rejecting the scorch hypothesis. Like any other hypothesis, there is always the possibility of modifying to accommodate new facts, rather than rejecting outright. An idea I have been toying with for some time is that the linen may have been impregnated with something that acts as a thermosensitizer, making it easier to acquire a “scorch” mark at a lower temperature. The effect that springs to mind is that of “invisible writing”, e.g. using lemon juice or sodium carbonate. So it’s not impossible that one could end with an “impurity” idea not dissimilar to Rogers’, with the image on an “impurity” coating, but still needing direct contact with a hot template in order to get the thermal imprint and the superficial scorching of mainly the highest fibres. In fact, I steeped some of my linen in lemon juice last night and when it’s dry will see if it’s more receptive to low temperature scorching than ordinary untreated linen.

        Interestingly I have come across a very recent paper (2011) that challenges the idea that hot lemon juice and its acids attack the cellulose. It says lemon juice on its own can account for the brown colour. It would be interesting to see if I can get an image on linen WITHOUT that pesky green fluorescence!

      • Adrie says:

        Hi Matthias and all. The green fluorescing donut-shaped burnmarks, located at 11-12, that is in the middle of the cloth on both sides of the two longitudinal scorched folds (see ), were indeed from the 1532 fire. Guerreschi and Salcito determined that they were in the bottom layers of the folded cloth when it lay in the reliquary ( ). They reproduced the entire scorch pattern with one single scorch motion on a Shroud-wise folded cloth, and their lightest scorches appeared where the green fluorescing ones are on the Shroud (p. 1-3 with figures).
        The difference in color of the ‘red’ and ‘green’ scorches seems to be the result of a different combination of oxygen, water, contact time, pressure and temperature. Guerreschi and Salcito wrote “We also observed that, due to the weight of the object, the pyrolysis tended to diminish in the part directly in contact, continuing in the free terminal part due to the supply of new oxygen, leading to the enlargement and therefore the triangular shape of the burns.” (p.3)

    • Adrie says:

      Hi Hugh and Colin. Re 3: Miller&Pellicori reported non-fluorescing scorches (or stains resembling scorches): “There is a series of holes through the Shroud cloth (through which the reinforcing backing cloth sewn to the Shroud after the fire can be seen). The densely burned borders of these burned holes show no emission. Where the more lightly scorched material matches the appearance of other scorched areas (around patches, for example), the fluorescent appearance is quite different, that is, no emission is seen. The different appearances might relate to different generation mechanisms. […] around the patches, the scorches display shading in red emission. These scorches appear different from the burn holes.”(Ultraviolet fluorescence photography of the Shroud of Turin, p.77, fig 5 dorsal area B-E, 4-6). I don’t know whether they mean the so-called ‘poker holes’ or the tiny holes visible in the middle of the buttocks area.
      In the next area: “Two small circular stains at C-7 and D-7 are mirror images and visually resemble weak scorches. In fluorescence these stains are absorbing.”(p.79, fig 6 dorsal midsection area B-E, 7-9)
      In still another area: “Scorches show red fluorescence except for those associated with the sets of three holes which have heavily burned borders. Plumes of pyrolyzed materials pointing toward the feet are seen associated with the burned holes. At 19 the plume pointing toward the hands fluoresces red. Some shading from red to yellow fluorescence can be seen.”(p.82, fig. 9, ventral hands and thighs B-E, 16-19). Here the three ‘poker holes’ are definitely meant. For locations see: and (lowest row is A, highest row is F).

      The explanation for the ‘poker holes’ is not definitive. Legrand thought about incence causing them, Flury-Lemberg about concentrated acid ( p. 9). The acid idea has been contested, says Barta ( p.1) (I read this contestation once, somewhere, but didn’t bookmark it). Rogers said the borders looked like pitch, but did no chemical analysis; “his term “pitch” was intended to apply to pine sap or something of a balsamic origin” ( ). “The hypothesis that these holes were burned through with a hot poker is probably incorrrect. Close inspection of the peripheral areas reveals a foreign material there, resembling pitch. The radiographs also show high density structures that supports this observation. This earlier damage may have resulted from burning pitch that perhaps fell onto the Shroud from a torch.” Schwalbe, L. A., and R. N. Rogers, Physics and Chemistry of the Shroud of Turin, a Summary of the 1978 Investigations, Analytica Chimica Acta 135 (1982), pp.3-49, p. 47, note 7.

      • Adrie says:

        Note: the cited “At 19 the plume pointing toward the hands fluoresces red. Some shading from red to yellow fluorescence can be seen.”(M&P, p.82, fig. 9, ventral hands and thighs B-E, 16-19) does not refer to the ‘poker holes’ at the height of the hands (= at 16-17), but to the fold scorched in1532 at the heigth of the thighs (= at 19) (see ).

  5. colinsberry says:

    Hello again Matthias

    edit: I wrote this before seeing Hugh’s reply to you, which shows the two of us are thinking along much the same lines)

    Most certainly it is, i.e. a problem for the scorch theory. It is hugely embarrassing! But bring it on, that’s what I say. Science – real science that is – thrives on embarrassment. Who knows, it may be Hugh with his eBay uv lamp and his school laboratory (which beats my kitchen) who will crack this one.

    All I have at the moment are some fragments of information and embryonic ideas. Someone has suggested that the green fluorescence of heated linen is due to furfural, I have just looked up the boiling point of furfural. It’s 162 degrees C. That means it will have an appreciable vapour pressure at normal temperature and pressure, which in turn means it will very slowly evaporate. So it could be that the Shroud, if a medieval forgery, and made by scorching, was also fluorescent to begin with, but has gradually lost ifs furfural and its fluorescence over the centuries.Without a time machine, that’s a tricky one to test… Maybe Hugh could put his scorches back in an oven at, say, 100 degrees and see if the fluorescence gradually disappears …

    Any chance you would be willing to venture an opinion on my response here to Thibault’s attempts to exclude scorching? Would you agree that Thibault has ‘shot his bolt’ so to speak with hardware that was simply not up to the job? The Other Site seems not to be aware I have responded judging by some comments, perhaps because the site’s catcher is putting the spotlight on some other recent posts and comments of mine instead. But I’m not going there, oh no sir, just to be branded an upstart, ignoramus or worse by he and his crew of know–all regulars….

  6. Adrie says:

    Re: Hugh 4) (I guess you mean the reddish fluorescence of most Shroud scorches). STURP members Miller and Pellicori wrote: “Laboratory-produced scorches emit a bright greenish-yellow fluorescence if they were produced in air and reddish if produced under conditions of limited available oxygen. The scorches associated with the fire of 1532, during which the Shroud was involved, attest to the rapid consumption of the available oxygen. Their reddish emission is probably due to furfurals, which can be produced under such conditions. Linen lightly scorched by a soldering iron in air shows the green-yellow emission, often distributed in plumes of deposited pyrolysis products. We demonstrated in one experiment that the material of the plumes could be transported by water, but the underlying scorched cellulose retained a bright yellow-green fluorescence.” (Miller, V.D., and S.F. Pellicori, Ultraviolet Fluorescence Photography of the Shroud of Turin, Journal of Biological Photography, Vol. 49, No. 3, July 1981, pp. 71-85, p. 84)

    It seems the Shroud also has some green fluorescing scorches: “At E and B and at patches 11 and 12, red fluorescing scorched areas are obvious. The brightly fluorescing yellow-green donut-shaped areas to the right of patch 11-12 at E and B appear to be scorches. They are mirrored elsewhere at symmetrically located fold sections.” (Ibid., p. 80)

    It still is confusing why you didn’t reproduce the reddish fluorescence. Perhaps because there was too much water around, that could not escape from the tinfoil and that was driving out the air in the testtube?? Just guessing…

  7. Hugh Farey says:

    Hi Adrie. I tried two different experiments to try to reduce the oxygen.

    1) Fold up a 4x4cm square of linen into a little block 1x1cm and 16 layers thick. Wrap it in aluminium cooking foil till the foil is 10 layers thick. Wrap the ends of the tinfoil tightly around the package and squash tight. Hold the whole thing over a Bunsen for 5 seconds. The package bulges a bit. Unfold. The linen is scorched on the outer faces and edges, but fluoresces as greeny-yellow as any other.

    2) Heat 3ml of water in a test tube till it is boiling. Push a 3x3cm piece of linen into the tube. When it begins to brown, remove the burner. Allow to cool. Still greeny-yellow fluorescence.

    Do you happen to know if the explanation for the red on the shroud is anything more than an educated guess? Has anyone produced red fluorescence by experimentation? If so, how?

    • Adrie says:

      Hi Hugh. Miller&Pellicori’s paper only said “laboratory-produced scorches” emit reddish fluorescense “if produced under conditions of limited available oxygen.” From Heller’s book we learn: “Vern Miller’s experiment at the acadamy with burning linen in a limited-oxygen atmosphere had produced a furfural-type material, which fluoresced in the ultraviolet. This jibed with the ultraviolet reflectance spectra [sic] of the Shroud itself.” (J.H. Heller, Report on the Shroud of Turin, p.175). It doesn’t say how he produced the scorches, or whether the “furfural-type material” in them was experimentally determined.

  8. colinsberry says:

    Hello Adrie

    Snap. I’ve just finished discussing oxygen deprivation as the second instalment of my critique of TH. I suspect that conditions are essentially anaerobic under a new scorch from under a heated template:

    It could be that later exposure to air and oxygen produces a delayed secondary oxidation that then destroys the fluorochrome, whatever that may be, formed by anaerobic pyrolysis, though evaporation alone would account for loss of furfural.

    To be honest, I consider attempts to rule out this or that mechanism of image-formation on the basis of fluorescence (not) remaining after many centuries to be more in the realms of witchcraft than of science…

    Why did WordPress not provide a Reply tab under your comment I wonder?

  9. Adrie says:

    Hello Colin,

    Just now I tried to post a very long comment, twice, but they didn’t appear. If you’ve received them, could you only post the second one? Thanks.

  10. Adrie says:

    Thanks for your e-mail address, Colin. I tried posting the comment again, and now I received the error message: “Duplicate comment detected; it looks as though you’ve already said that!” So, it’s probably on its way… The second post still would be enough…

    (ed: Adrie’s comment below has now arrived at last by email):

    Hello Colin,

    This is a late and long reply to your comment about essentially anaerobic conditions for a new scorch from under a heated template. I’ve been pondering on it as well, and thought that the ‘green’ scorches on the Shroud may have been aerobic, even though at the bottom of the reliquary, because the bottom layer of the folded cloth was only about half the length of the folded package. There was a furrow with oxygen-rich air under the cloth (see top right figure on p. 3 of G&S). The heated object scorched the upper layers “in an oblique manner” (G&S p. 2) (probably initially aerobic, but when the object moved down more and more anaerobic), but when it reached the bottom layer it reached the furrow with oxygen and scorched the donut shaped marks with green fluorescence. The object couldn’t move further down, as it had reached the bottom of the reliquary, so any new lack of oxygen would not have resulted in replacement of the ‘green’ donuts by larger holes with ‘red’ scorch borders. And the reliquary at some point opened up, admitting the water that caused the small watermarks and eventually new air. Rogers’ book says that Pellicori reported that “the margins of the scorches fluoresced in the green, entirely different than the background of the Shroud”, but doesn’t give a reference (A Chemist’s Perspective on the Shroud of Turin, p. 20). Pellicori’s observation would corroborate Miller’s experiments, in which the ‘red’ scorches were anaerobic, and the ‘green’ ones aerobic. “Modern linen can be artificially aged by baking at high temperature (125º-150º C) to the point where its reflected color and fluorescent emission approach those of the Shroud”; “a 5-h air bake at 150ºC. […] the time/temperature exposure used reproduces the color of the Shroud” (M&P, Ultraviolet fluorescence, p. 84; Pellicori, Spectral properties, p. 1916-17, 1919). Here Miller and Pellicori refer to the background color of the Shroud, so, the obtained visible color was lighter than that of the Shroud image, but the obtained green fluorescence was stronger than the fluorescence of the image: the image fluorescence is much less and peaks at a slightly longer wavelength than that of the background (Gilbert&Gilbert, Utraviolet-visible reflectance and fluorescence spectra, p. 1934). Adler wrote: “The background cloth shows a light greenish yellow emission not typical of other known old linen cloths and perhaps suggesting the presence of some type of thin coating of a fluorophore on the original linen” (Chemical and Physical Aspects, p. 13).

    Rogers and Schwalbe wrote in 1982: “Miller and Pellicori produced light sources [sic] on modern linen in an atmospheric environment with a hot soldering iron. They found that scorches produced at various temperatures on both dampened and dry cloth all fluoresced yellow-green under ultraviolet radiation. Further experiments showed that the fluorescent compounds were quite water-soluble, although even after repeated rinsing, the scorched areas retained their fluorescent properties. In addition, they demonstrated the stability of the fluorescent compounds by baking the samples at 145ºC for six hours. Pellicori recalls that the Shroud image itself does not fluoresce measurably. In view of the results of these scorch studies, he feels that it is unlikely that the image was produced by scorching, for otherwise there should have been some characteristic fluorescent behavior observed. These results draw the “air” scorch hypothesis into serious question; however, it was chosen to leave the matter as an open question for now. Before the non-fluorescent property of the image is taken as conclusive evidence against scorch hypotheses generally, the conditions and reactions that are involved in the formation of these compounds must be better understood. Future studies should include many of Miller and Pellicori’s original experiments on actual Shroud threads” (Physics and Chemistry, p. 27).

    In 2004 Rogers’ book revealed that furfural was found in Shroud scorches but not in image areas. “A positive Seliwanoff’s test for pentoses or furfural was obtained from scorched fibers of the main Shroud, while non-scorched non-image fibers gave a negative Seliwanoff’s test” (Rogers, A Chemist’s Perspective, p.40). STURP’s sample mappings show that no tape samples were taken from the green donuts, three from light scorches, perhaps partly from their green margins, one from a light or dark scorch, and one from a dark scorch. Rogers: “If the image had been formed by a scorching-type, high-temperature reaction, some pyrolysis products of linen, including furfural, might still be present. The detection of pyrolysis products would have been fairly conclusive evidence for an image-formation mechanism; however, the absence of such products would prove nothing. I got no test with Bial’s reagent, so I also tried Seliwanoff’s test for furfural. […] I could not prove the presence of furfural on image areas; however, it was worth the effort to try” (Ibid. p. 39-40).

    Rogers said furfural polymerises over time: “I also tried Seliwanoff’s test for furfural. It gives a nice, bright red color with furfural, but it gave no test with fibers from a light Shroud scorch. Furfural polymerises over time to form a dense, dark polymer that does not give the test. Polymerization is faster when the reaction is catalyzed with some common impurities, and it can be slowed with inhibitors. I could not prove the presence of furfural on image areas” (Ibid. p. 39-40). As he also said “A positive Seliwanoff’s test […] was obtained from scorched fibers of the main Shroud” (p. 40), an explanation Rogers deems possible for the absence of chemically detectable furfural in image areas is complete polymerisation there, as in one unspecified light scorch, but not in all scorch areas.
    The question it raises is whether polymerised furfural fluoresces, and if so, which color. This liquid furfural absorption spectrum peaks at 92 nm, and this furfural solution absorption spectrum peaks at 270 nm. For comparison, this (liquid) vanillin absorption spectrum peaks at 230 nm and from 280-320 nm, but this fluorescence emission spectrum of a vanillin solution under 360 nm UV excitation peaks at 425 nm (violet): “Fig. 3: […] The excitation wavelength was 360 nm. […] For comparison, the fluorescence emission spectra of 200 μM vanillin (spectrum d), 8 μM free enzyme (spectrum e), and […] are shown in B” (subscript of Fig. 3). Likewise, because a substance cannot emit a shorter wavelength than it absorbs, a furfural solution under 360 nm excitation would also have to fluoresce at longer wavelengths than 360 nm or equal to it. Such a spectrum would be comparable to the UV/Vis spectra of the Shroud made under 366 nm excitation, and to the photos taken under 335-375 nm excitation (Pellicori, Spectral properties, p. 1919). Then, furfural’s being embedded in scorched linen, and polymerisation of furfural, would change the molecular orbitals and their energy levels, so it would change the absorption and fluorescence wavelengths too. I suppose this change is toward longer wavelengths, as for example this absorption spectrum of a furfural and potassium biphthalate polymer (Fig. 12 c) shows it peaks at a longer wavelength than the spectrum of simple furfural (Fig. 12 a). This furfural-naphthol resin (fig. 4) emits a 680 nm red fluorescence under an “assigned excitation” of 680 nm (table 1). And these “carbon dots” of polymerised and aromatised furfural compounds – a “furan resin” (p. 2) – strongly fluoresce blue under 405 nm violet excitation and green under 488 nm blue excitation (photos p. 11-12). Mere furan, the fluorescing ring in all these substances, absorbs from 200-230 nm when liquid.
    So, furfural in linen, also polymerised furfural, does fluoresce and might fluoresce green or perhaps even red (as I see it now, but I’m not a chemist). As there are red fluorescing scorches (with green-yellow margins) in the image area (Adler, Chemical and Physical aspects, Fig. 2), only a fluorescence quencher that was applied after image formation and removed by the 1532 AD scorches might explain the absent/weaker fluorescence of the image, but this seems improbable (but again, I’m not a chemist).

    When trying to prove that the Raes/radiocarbon sample was from a repair in the main Shroud, Rogers wrote that the anearobic pyrolysis mass spectrometry data of five different image areas showed no early furfural release (it appeared only when hydroxymethylfurfural appeared, or near to that, “For example, figure VIII-3 shows a mass spectrum that was taken when the first decomposition products started to appear over a sample of image fibers.” Rogers, A Chemist’s p. 54; Fig. VIII-3 is Fig. 1 in Pyrolysis/Mass Spectrometry; furfural is at m/e 96, HMF at 126), whereas the (lightly scorched) Raes sample did show early furfural release without HMF: “furfural appears relatively early, and it disappears quickly” (Rogers, A Chemist’s, p. 57, and Fig. VIII-4 which is Fig. 2 in the online PMS article). That the Raes corner is lightly scorched is shown by
    1. its fluorescence (Antonacci, 2005, p. 5-6: “After studying ultraviolet fluorescent photographs taken of the Shroud, STURP’s chief photographer Vernon Miller and Alan Adler confirmed over 15 years ago that the radiocarbon site was in the midst of a scorch mark and at the edge of a water stain.”)
    2. the FTIR data of the radiocarbon sample having scorch characteristics (Adler, Selzer and DeBlase, Further Spectroscopic, p. 98)
    3. its positive Bial’s reagent test for furfural/pentoses (Rogers, A Chemist’s, p. 39)
    4. its starch gum coating – not gum Arabic for lack of proteins (Rogers, Scientific Method, p.17-20 – Adler, p. 4).
    The Raes thread’s early release of furfural without HMF could be explained by it having been scorched at a temperature above the pyrolysis threshold of hemicellulose (which produces furfural from xylose) but below the pyrolysis threshold of cellulose (which produces HMF from glucose), i.e. below ca. 315ºC, as you suggested in this blogpost (see also these TGA pyrolysis curves of hemicellulose, cellulose, and lignin; btw “lignin was more difficult to decompose, as its weight loss happened in a wide temperature range (from 160 to 900 °C) and the generated solid residue was very high (∼40 wt.%)” Fuel article).
    Note that not even one irrefutable scorch sample from the main Shroud was tested with PMS: the tested 6BF sample is classified as “light scorch” by Rogers (PMS article, p.2), but is called “Blood Flow (Approx. Test Point)” by the STURP sample list, and “Blood image, front, lance area” by Heller&Adler, who called sample 6AF, taken a bit closer to the scorch than 6BF, “Blood-scorch image margin” (A Chemical Investigation, p. 49). Assuming that Rogers managed to find a lightly scorched fiber on sample 6BF – distinguishable by a scorched medulla (Scientific Method, p. 8-9) –, it would have showed the simultaneous furfural and HMF release (or perhaps even later furfural release if polymerised) of a linen fiber scorched above 315ºC (all its hemicellulose plus overabundant cellulose being scorched), for in his comparison of all tested samples, including the one from the “Edgerton modern” linen, which was lightly scorched by ironing, and then bleached again (Rogers on Maillard reaction, p.3), Rogers doesn’t talk about temperatures anymore, but only says that among all “product ratios” (furfural/HMF) the Raes sample “was unique” (PMS article, p. 6). In fact, Rogers doesn’t give any absolute temperature.
    Anyway, for testing the scorch hypothesis the question is: could a very high degree of furfural polimerisation in image fibers have retarded its furfural release to near that of HMF from unscorched cellulose? For the above mentioned furfural polymer (“a furfural and potassium biphthalate-based resin”) “The highest temperature at which the polymer melting process occurred was found to be 202.01 °C, which far exceeds the boiling point of pure furfural (161.7 °C)” (par. 3.1.7.). So, it seems the answer is: yes, it might perhaps have retarded the furfural release that far. But then, the furfural polymer would probably still be fluorescent…

    1) Anaerobic model (red fluorescence): (red) Shroud scorches with the same visible color as the image fluoresce red, even in the image area, while the image doesn’t fluoresce noticably. So, sensitising the cloth is no option in the anaerobic model. An ‘image-only’ fluorescence quencher to explain the difference seems improbable. Assuming it’s not there, the scorch image would have to have lost its fluorescence, by oxidation or evaporation, in 200 or more years after having kept some or all of it in 500 years. Anaerobic Shroud scorches fluoresce red + anaerobic PMS of linen produces furfural and hydroxymethylfurfural + furfural is fluorescent (and HMF probably too because of its furan ring) => furfural and/or HMF in scorched linen probably fluoresces red. The image doesn’t contain free furfural or HMF, while some light Shroud scorches do contain furfural. So, the image would have to have lost its free furfural. Rogers says furfural would rather polimerise than disappear by oxidation or evaporation, but polimerised furfural probably fluoresces.
    2) Aerobic model (green fluorescence): the Shroud image fluoresces much less and a slightly warmer color than the ‘greenish’ background. On pure non-fluorescing modern linen the Shroud’s visible image color cannot be reproduced immediately without producing green-yellow fluorescence (Hugh 1). This fluorescence even appears at lower temperatures than a visible scorch color (Hugh 2). The green scorch fluorescence doesn’t disappear with aging (air-baking/500 years). As air-baking/scorching produces green fluorescence ánd simulates aging, aging would rather intensify green scorch/age fluorescence. So, a scorch image should never have had green fluorescence (or at least scorching should have produced less than it took away). Pure linen becomes green fluorescent by air-baking above ca. 125ºC (M&P and Hugh 3). To produce a Shroud-like image color without (too much) green fluorescence one might use a sensitiser, as possibly present on the Shroud, and scorch below a certain temperature, perhaps below ca. 125ºC. But, as air-scorching and aging are basically the same process, in the centuries of aging the scorch would always be ahead of the background in this process, and have more green fluorescence than the background, until some kind of saturation takes place. Only a relatively strong cool-fluorescent coating would allow a scorch to take away this fluorescence and have a permanently weaker and warmer fluorescence than the background.

    Am I mistaken somewhere…?

    An alternative for a low temperature contact scorch is a (low temperature) electrostatic discharge (aka corona discharge or St. Elmo’s fire). Its image is dark/light-inverted, 3D-encoded, and superficial, as the Shroud image link1, link2, link3, link4, link5). The fourth article concludes: “From the IR results, we can say that C-O-C and C-O bonds are produced when CD is present and C-H bonds disappear. We propose that a kind of slow combustion process occurs during CD that forms the image on linen” (p. 2589). It is said that a new CD image, that still has to become visible by aging/air-baking, has a “lack of fluorescence” compared to the blue fluorescing background of “new, but not bleached linen”, i.e. “manufactured as the old linens were” (link2, p. 17; link1, p. 12; cf. link1, p. 9 fifth -, and p. 19 at 1), but its image fluorescence does look green-yellow (see link1, Fig. 15).
    It seems that a very light aerobic contact scorch and a CD are mutually not all that different in terms of fluorescence. After an initial inversion from the relatively strong blue linen background fluorescence to the weaker green-yellow fluoresence of the ‘undeveloped’ CD image, the developed visible image would later, after air-baking or aging, probably have a stronger green fluorescence than the background. In that case, also a CD would need a cool-greenish fluorescent coating to explain the weaker and warmer fluorescence of the image when compared to the background after centuries of aging.

    A coating of retrograded starch including a dilute acidic Madder dye (as batch-uniforming color and optical brightner) might keep most of its fugitive fluorophores alizarin and purpurin, if it was glazed by firmly rubbing it with a glass ball or slickstone, such as this Viking-type linen smoother or the Dutch smoothing balls from the 8th and 9th centuries (“bollen uit de 8e en 9e eeuw”), to render it more dense and sealing, and thus dirt repellant and lustrous. Number B14 of the Shroud evidence list says “The TS linen has a lustrous finish (Rogers, 1978-1981).” This is another corroboration for the Shroud being a robe as Herod’s ‘estheta lampran’ (Luke 23,11 WH), literaly “shining robe” (Bible in Basic English), “brilliant robe” (HCSB), “glistening clothing” (LEB), also translated as “white cloak” (WYC) and “kingly robe” (NCV) (BibleGateway). The sealing starch finish would also have retarded the aging of the very tightly woven linen Shroud (evidence B5). Saponaria Officinalis, also called struthium, was not detected on the Shroud: “I could not prove that the cloth had been washed in S. Officinalis. Only the fluorescence evidence remains to suggest the use of struthium” (Rogers, A Chemist’s, p. 40), but Madder was chemically detected on the Raes sample (which isn’t a repair) inside the coating and as lake particles, and microscopically recognized as lake particles on the main Shroud (Internal selvedge in starched and dyed temple mantle, par. 2.3 and 2.4 (updated)).

  11. colinsberry says:

    Oh dear. Your long comment has still not been received, Adrie. It’s not clear why not (my filters seem correctly set to allow your comments through, as shown by the 2 already received this morning). If it does not appear in the next 5 or 10 minutes, then try emailing? On arrival I will then add it as an Edit to your most recent comment. If not convenient right now, then send later, but I have to go out soon, and won’t be able to display it until after I get back.

    Update: your comment has now arrived in my email inbox. I’ve done as suggested and added it to your comment as an Edit. When I read it, I might suggest that you hopefully consent to having it displayed it as a “Comment promoted” type of posting, in view of its length and the time you must have spent on preparing it. I’d hate to think it got overlooked through being buried in Comments, even current ones.

  12. colinsberry says:

    The only comment I have received is the short one that just arrived, Adrie. I have also checked the email inbox that notifies me of new comments, and your long comment(s) is not there either. I do hope you kept a copy.

    If you don’t succeed in sending it, you could always try sending as an email.

  13. colinsberry says:

    I’ve read it through briefly, Adrie. It’s very impressive – I doubt there are many who have thought through the alternative mechanisms in this level of detail. But that is the problem as far as a blogsite like this is concerned. There’s a surfeit of detail – it will go over most readers’ heads (and this ex-researcher who has worked with tracking fluorescent chemicals was struggling to cope in places).

    Rather than display in its present form (as a guest posting) might I make a suggestion. Re-structure it. Start by listing the alternative mechanisms by which scorching could conceivably produce fluorescent products. Then flag up the key variables (oxygen limiting/not limiting; temperature etc) You could make it one of those dichotomous tree diagrams. Then list possible products (furfural, polymerised furfural, others etc) Then add presence or absence of fluorescence quenchers, age-related effects (> or < 500 years), then show where fluorescent RED or YELLOW-GREEN products can or might be seen, or are seen, permanently or otherwise. Once folk can see at a glance the range of options, how fluorescence can either arise via scorching OR be subsequently lost, one can then overlay with present knowledge, where it exists, or there again be able to pinpoint precisely where there are gaps or uncertainties in the logic pathway.

    Sorry to sound like a pedant. That is the last thing I want. It's because your analysis is so IMPORTANT and TIMELY that I think we need to think about how best to display the detail without overloading the reader too soon with a surfeit of detail and complexity. Feel free to ignore some or all of my suggestions, which are off the top of my head. There may be much, much better ways of displaying the 'big picture'.

  14. Hugh Farey says:

    Can I add my support Colin’s appeal? I think I follow the theme of your post, but most of it is way over my head, and a tree diagram might help clarify the details!

  15. colinsberry says:

    Thanks Adrie. I hope you’re happy with that arrangement for now.

    There’s one point that I feel ought to be made whenever the topic of fluorescence comes up in connection with scorching and/or the Shroud – namely that one is seeing the ghostly signature of just one several possible pyrolysis products in a reaction mix that just happens to have a fluorescent chromophore. So it is like watching a soccer match under black (uv) lights in which just one or two players are visible on account of having the right kind of shirt.

    I have to say I have strong reservations about furfural surviving more than a few decades, never mind centuries or millennia. Apart from the likelihood that so reactive a molecule would or could polymerise, on account of that reactive aldehyde function, there is also the fact that it is a liquid at normal temperature and pressure with a finite vapour pressure. Its boiling point of 162 degrees C is actually lower than the most volatile constituents of diesel fuel (180 degrees and upwards). We all know that spilt diesel does (finally) evaporate. So too will furfural, unless it oxidises or polymerises first. (It’s said to yellow rapidly in air). Neither can I imagine its fluorescence surviving polymerisation if, as one presumes, the unsaturated aldehyde group is involved in polymerisation, since that leaves only the two double bonds in the furan ring for ease of electron promotion by uv light. I can’t help but wonder if it’s not a case of “looking where the light is” (I don’t know if you’re familiar with that analogy, of the drunk looking for a dropped coin in the dark on the opposite side of the street from where he dropped it, because that was the side with the street lamp). “Looking where the light is”. Probably 95% of science fits that description…

  16. Adrie says:

    Hello Colin,
    Again I tried to post a comment that is too long for posting directly. I’ll send it to you be email. Could you please paste it in this comment?

  17. colinsberry says:

    Hello Adrie

    Will do, but it will have to wait a couple of days I’m afraid. I’m travelling, and having trouble logging into that particular email account.

    If urgent, you could maybe post as separate instalments.

    • Adrie says:

      No, it’s not urgent. It can easily wait a couple of days. Have a nice trip!

      (ed: here is the comment that Adrie sent that was apparently rejected by WordPress software on account of its length. I’m copying and pasting it from his her email that I have finally been able to open, now I’m back on my own laptop):

      “It seems to me that furfural in scorched linen isn’t comparable to a fluid that evaporates. In newly scorched linen furfural is ‘in solution’ in its surrounding other pyrolysis products and other non-pyrolysis products (all organic substances), and there, its very reactive aldehyde group would sooner or later polymerise with them. I found a number of quotes about furfural evaporation, showing that it is most prominent when furfural is in water or is a pure fluid on/in moist soil, and less prominent and even uncertain when it is a fluid on/in dry soil (which would contain little organic material): “With the water vapor can be volatile, benzene aldehyde odor” (Chinese entry); “Furfural is produced from annually renewable agricultural sources /containing pentosans[…] In all processes, raw material is charged to the digestor and treated with strong inorganic acid. High pressure steam is introduced through the mass and, after attaining operating temperature and pressure, furfural is steam distilled”; “If released to soil, furfural is expected to have very high mobility based upon an estimated Koc of 40. Volatilization from moist soil surfaces is expected to be an important fate process based upon an estimated Henry’s Law constant of 3.8X10-6 atm-cu m/mole. Furfural may volatilize from dry soil surfaces based upon its vapor pressure”, “Volatilization from water surfaces is expected to be an important fate process based upon this compound’s estimated Henry’s Law constant” (PubChem, Methods of Manufacturing; Environmental Fate and Exposure Potential).
      So, in dry scorched linen, containing only carbohydrates and other organic material, furfural would evaporate (at best) slowly and have the chance to polymerise immediately. Furfural “Forms condensation products with many types of cmpd, phenol, amines, urea, etc” (Ibid., Chemical and Physical Properties; condensation is polymerisation by losing a small molecule).
      As regards the speed of polymerisation: Rogers said that after a “burn test” on modern linen “Condensed cellulose pyrolysis products form an intensely fluorescent ring around the center of heating” (Scientific Method, p. 3-4, caption fig. 2). He meant ‘cellulose’ that had been pyrolysed and then had chemically condensed. In the text he speaks about “the chemically reducing and reactive pyrolysis products (formaldehyde, furfural, organic acids, CO, etc.)” (p. 4). Here Rogers’ use of “cellulose” and “furfural” should include hemicellulose and hydroxymethylfurfural. (Besides, it seems to me the fluorescent ring was scorched aerobic.) Anyway, Rogers here says polymerisation/condensation of furfural takes place very soon after scorching (not only after decades of evaporation), and that such a polymerisation doesn’t inhibit fluorescence.

      Also, furfural’s chemical structure shows that furfural after polimerisation by bonding at its aldehyde group would still fluoresce. The aldehydegroup of furfural is its only difference with furan, which has just a single hydrogen atom instead of the aldehyde group. The ring of furfural is equal to the ring of furan, and this ring has only two double bonds. So, as furan fluoresces, a furfural polymer, having changed or lost its complete aldehyde group but still having this same furan ring, would also fluoresce. At least some furfural polymers, bonded by furfural’s aldehyde group, fluoresce measurably, such as the furfural-biphthalate resin: its chemical structure shows a resin of furfural bound by its aldehyde group (Scheme 2). Its fluorescence is a bit weaker than that of pure furfural, but still much stronger than the hardly fluorescent biphthalate (Fig. 12). Also in the furfural-naphthol resin the aldehyde group of furfural has bonded to naphthol (Scheme 3), and then there was condensation of the naphthol-furfural molecules at the oxygen atom of the (former) aldehyde group, so, also here the furan ring has been preserved (Scheme 5). This “condensed furfurylol Naphthol pigment” fluoresces and, as its relative intensity is stronger than that of mere naphthol (Fig. 4), the furan ring still contributes to the fluorescence of the polymer.

      So, from the above, it seems that furfural in scorched linen polymerises before evaporating, and it is certain that polymerised furfural still fluoresces. But, in order to not only search where the light is, let’s assume there are more fluorophores in anaerobic scorched linen than only the furan-type. The question then is, whether the furan-type causes the red fluorescence of the anaerobic scorches.
      Furfural is produced in an anaerobic (= red) scorch/pyrolysis (PMS article, p. 2) and was detected in Shroud scorches, probably red (= anaerobic) ones (Seliwanoff’s test, A Chemist’s, p. 40). Pellicori, Rogers, and Soran, implicitly said furfural fluoresces red: “The fluorescence in the scorched areas is apparently due to the furfural pyrolysis products. (R.N. Rogers and D. Soran, Los Alamos Scientific Laboratories; personal communication” (Spectral properties, 1980, p.1919). Miller and Pellicori wrote “The scorches associated with the fire of 1532, during which the Shroud was involved, attest to rapid consumption of the available oxygen. Their reddish emission is probably due to furfurals, which can be produced under such conditions”, and also wrote “The visually dark-brown burns fluoresce brownish-red. The color reddens as the scorch density decreases. Comparable to pyrolysis products, produced under limited oxygen combustion, such as furfurals” (Ultraviolet fluorescence, 1981, p. 84, 75). The chemist Heller finally did declare that Miller’s experiment “with burning linen in a limited-oxygen atmosphere had produced a furfural-type material, which fluoresced in the ultraviolet. This jibed with the ultraviolet reflectance spectra of the Shroud of Turin” (Report on, 1983, p. 175). So, according to Pellicori, Rogers, Soran, Miller, and Heller a furfural/furan-type material in anaerobically scorched linen fluoresces red or comparable to red.

      If furfural doesn’t cause the red fluorescence of the Shroud scorches, there would have to be a stronger red fluorescence of another unknown fluorophore produced by anaerobic pyrolysis of linen. In order to produce “highly fluorescent carbon dots” from “hydrothermally treated” orange juice the fluorescent products (“Furfural like compounds, aldehydes, ketones”) were separated from the non- or less fluorescent products (“Acetic acid, Lactic, Propenoic, Levunilic and formic acid”) (p. 1-2, Fig. p. 2): “The aqueous solution was centrifuged at 3000 rpm for 15 min to separate the less-fluorescent deposit” (p. 1). When discussing the PMS of linen, Rogers said “The major products of the thermal decomposition of cellulose and other carbohydrates in the absence of oxygen are formaldehyde, carbon monoxide, furfural (2-furaldehyde), hydroxymethylfurfural (5-hydroxymethyl-2-furaldehyde), levulinic acid (4-oxopentanoic acid), and 3-pentenoic--anhydride” (PMS article, p. 2). Except the furfural-types, non of these have rings, let alone aromatic rings (except perhaps the 3-pentenoic--anhydride, which chemical structure I haven’t found, but which is probably similar to pentanoic-anhydride, which is not a ring). So, these other products probably wouldn’t be (strongly) fluorescent. Levulinic acid was indeed separated as less fluorescent than furfural in the carbon dots production. Either formaldehyde (“formaline
      solution 37%”) or a “Formaldehyde pigment” fluoresces or both do (note the inconsistencies between table 1 and fig. 4), but if formaldehyde fluoresces it apparently doesn’t fluoresce enough to be detectable by its fluorescence without this “fluorogenic dye”. Besides, formaldehyde, having only one double bond, would fluoresce less than formic acid, which has two double bonds and fluoresces less than furfural (see carbon dots production). The five-carbon-plus-one-oxygen rings from pyrolysed xylan/hemicellulose, that you showed, only have one double bond, and thus probably don’t fluoresce stronger than furfural either.
      So, it seems to me that it is very likely that the red fluorescence of the anaerobic Shroud scorches is caused by their detected furfural-type fluorophore.

      An anaerobic scorch produces a) red fluorescence and b) furfural that c) fluoresces red. The red fluorescence (a) and the furfural (b) don’t disappear in 500 years, and furfural will always fluoresce, also when polymerised (c), and most probably causes the red fluorescence of the Shroud’s anaerobic scorches. The image has neither red fluorescence (a) nor detectable furfural (b) nor polymerised furfural for lack of red fluorescence (c).
      The image has a reflectance of the same visible color and intensity as anaerobic scorches, and in some areas is replaced by them, so,
      1) a sensitizer – which lowers the temperature at which the chromophore can be produced –
      would have affected image and scorch equally and thus, by itself, can’t explain the different fluorescence and furfural content
      2) an ‘image-only’ fluorescence quencher – i.e. that can be removed by scorching –, even if it existed and had been applied, wouldn’t explain the different furfural content
      3) if the chromophore can be produced anaerobically (perhaps even latently) at a lower temperature than that at which the fluorophore furfural is produced, a lower anaerobic pyrolyis temperature and longer pyrolysis time for the image might produce the image’s different (less red) fluorescence and (lower) furfural content in combination with a visible color and intensity equal to that of the red scorches. But even then, to be consistent with the Shroud, both the image-scorches and the red 1532 AD scorches should also have a much weaker and slightly warmer fluorescence and darker visible color than the background after centuries of aging.

      Still complex. I wish I knew what is the green-yellow aging-fluorophore and how its production depends on temperature/time. And it would be great to know if anaerobic scorching takes away (some of) the light blue fluorescence of lignin, and also to know the temperature/time dependency of this process, and also that of the loss of blue fluorescence in aerobic scorching.

      On the other hand, PMS did not detect lignin in Shroud samples (not only single fibers from the main Shroud but also “Raes fibers” = “ample material from the Raes sample”, and from the main Shroud’s ‘Zina thread’, see A Chemist’s, p. 57, PMS article p. 2, and Studies on, p. 192). But the same PMS did detect lignin in modern-primitive linen: “Mass spectrometry […] There is a significant difference between the Shroud and the modern-primitive samples. The latter were found to contain lignin” (Physics and Chemistry, p. 14). Also microchemical spot tests for vanillin (present in and slowly disappearing from fresh lignin (Scientific Method, p. 16), did not detect vanillin in Shroud samples (“No samples from any
      location on the shroud gave the vanillin test”, Studies on, p. 191), but “The Holland
      cloth and other medieval linens gave a clear test” (Ibid. p. 190). Nevertheless, the peak at ca. 435 nm of the fluorescence spectra of lignin solutions probably under 337 nm excitation (p. 10, and p. 3, Fig. 1; “337 nm was used as an excitation source for the experimental data shown in FIGS. 2 and 3”) coincides with the peak at ca. 435 nm of the fluorescence spectra of all Shroud samples, especially those of the background: “Figure VIII-2: Spectral fluorescence of four clear areas of the Shroud with excitation at 365 nanometers. Maximum fluorescence is at about 435 nanometers” (A Chemist’s Perspective, p. 51) ; “When the photoelectric data are convolved with the scotopic response curve and normalized (Fig. 9), it becomes obvious that the background linen itself is responsible for the measured response on the blood and image areas, since there is an identical wavelength characteristic” (Spectral properties, p. 1919).
      Absence of lignin and of its fluorescence would lead us back to (the necessity of) a fluorescent coating on the Shroud (cf. comment Nov. 13). The absorption spectrum of alizarin – the main colorant of Madder – also has a peak at ca. 435 nm, and “For many fluorophores the absorption spectrum is a mirror image of the emission spectrum. This is known as the mirror image rule.”

  18. colinsberry says:

    Here’s a link to a meaty comment from Adrie regarding furfural that should have appeared earlier (WordPress apparently blocks comments that exceed a certain length, so I have cut-and-pasted it from Adrie’s email.) Beware: Adrie takes no prisoners… 😉

    • Adrie says:

      Thank you very much, Colin, for the posting and flagging-up of my comment. It’s very kind of you. I guess I should have mentioned it earlier, as my name Adrie doesn’t betray it, but I’m a woman. But I also listen to “his” 🙂

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