Yup, each time I suggest that the Shroud of Turin is a heat scorch on linen, I get the same quickfire response from one or other Godfather of Shroudology. Paraphrased:
“Nope, you are entirely mistaken, you upstart you. We looked into that decades ago and dismissed it out of hand. The Shroud image does not fluoresce under uv light, while scorch marks do – even the 1532 scorch marks on the Shroud”.
For a flavour of the magisterial brand of Godfatherly prose, see this current link :
Since receiving that putdown on more than one occasion, and basically told to shut up, I have been careful to acknowledge the ‘fluorescence problem’ as recently as March this year. Why, I even acknowledged it in the title no less: ” One very good reason why the Turin Shroud could not possibly have been produced by scorching, and 10 even better ones why it could”
What’s more I have attempted some rather lame explanations, like maybe the Shroud image DID fluoresce when first formed, but has since undergone chemical changes over the centuries that have caused it to lose its fluorescence. Oops – the 1532 scorch marks are STILL fluorescent we are told. Well, maybe they need a few more centuries to exceed their shelf life too…. Nope, it doesn’t really cut the mustard does it? The good Dr.Heimburger offered us all another “out” in pointing out that high temperatures in that sealed reliquary in 1532 (sealed but for the melting of the silver in one or two hotspots) may have created different, i.e. largely oxygen-deficient conditions from those that created the initial Shroud image. See link.
But if I’m honest there is still a fluorescence roadblock that stands between me and getting the scorch model accepted (as a first step down a long rocky road as to what have might caused the scorching).
So why am I posting today, after a pause of some weeks? Well, I was checking a Ray Rogers paper today, and came across the following photograph describing some experiments he did to exclude applied pigment (“paint”) as an image mechanism.
Suddenly the penny dropped. Why did I not think of the answer to the fluorescence conundrum before, the one that has bugged me all these months? Leaving aside the ravages of age and entropy, it’s perhaps because I’ve been preoccupied with other matters, like my new interest in Stonehenge and Silbury Hill.
Irrespective, the answer has been staring me in the face. Rogers placed his paint specimens on what he describes as cellulose and, what’s more, cellulose that had been heated to a high temperature to produce that fluorescent halo that he attributed to chemically- condensed cellulose. (That’s presumably chemically-crosslinked cellulose, although there are other mechanisms proposed for formation of fluorescent pyrolysis products from cellulose, notably structures with aromatic rings systems that may or may not involve chemical condensation).
But there’s been a lot of new insights into the mechanism of the Shroud image since Rogers sadly passed away – ones that have rather tended to sideline cellulose, at least the majority of cellulose in linen that is located in the secondary cell wall, highly crystalline and therefore somewhat inert chemically.
Many, myself included , are inclined to the view that the Shroud image is formed on the remnants of the primary cell wall of linen fibres – that being the most superficial, i.e. exposed part of the linen fibres. What’s more the PCW is primarily loosely-packed non-crystalline cellulose and, more importantly, chemically-reactive hemicelluloses which, despite their name, are entirely different in chemical composition from cellulose. Their polymer chains have an assortment of sugars – notably 5 -carbon (pentosan) sugars that are chemically far more reactive than cellulose and thus more prone to the type of caramelisation reactions that are thought to have produced the Shroud image (after alternatives are ruled out, notably Rogers’ own Maillard reaction hypothesis, about which I shall say more later).
Now here’s some crucial information: hemicelluloses pyrolyse at much lower temperatures than cellulose, typically 220-315 degrees Celsius compared with 315-400 C. Note the bands while contiguous are non-overlapping.
So here’s my new explanation: pyrolysed hemicelluloses, produced at low temperatures, differ from pyrolysed cellulose, produced at high temperature. The 1532 scorch marks are thought to have been produced by molten silver (MPt very high – approx 962 degrees C for pure silver, somewhat less if alloyed) dripping onto the Shroud, which not only scorched but burned holes. The 1532 scorch marks fluoresce because they have pyrolysed cellulose; the Shroud image does not because it is pyrolysed hemicellulose.
A hypothesis should be testable, and have predictive utility. OK, so here’s my prediction. For anyone out there, with a lab and a suitable uv lamp, repeat my experiment with the horse brass but start with it hotter, above the pyrolysis temperature of cellulose.
Then repeatedly brand onto linen as it cools down to produce a range of progressively fainter images. I predict that not only will the fluorescence decrease with the image intensity (which should elicit few surprises) but that there will be a sudden cut-off in fluorescence at a temperature which corresponds with the lower limit of cellulose pyrolysis, but at which pyrolysis of hemicelluloses is still feasible.
Needless to say I have not been able to locate previously-published data on cellulose v hemicellulose pyrolysis and fluorescence, but shall continue searching.
Incidentally, there is another interesting fact in that Rogers paper that needs highlighting. In his desire to exclude paints and pigments, he said that protein could not have been used as binders, e.g. egg, because (paraphrased) “there was no additional nitrogen in the image areas”.
Verbatim: “The pyrolysis-mass-spectrometry analyses of individual fibers at the NSF Center of Excellence at the University of Nebraska was sufficiently sensitive to detect ppb levels of polyethylene oligomers that came from sample bags, but it did not detect any of the possible pigments or painting media. The pyrolysis-MS analyses did not detect any nitrogen-containing contaminants. This seemed to rule out glair (egg white) as well as any significant microbiological deposits. These results were confirmed by microchemical testing.
Oh dear. Ray Rogers’ own preferred Maillard mechanism would require the image areas to have additional nitrogen, i.e. as ammonia or as volatile organic amines (“putrescine”, “cadaverine” etc). Rogers effectively falsified his own pet theory! We all have bad days…
Belt and braces:
IMPORTANT UPDATE: ideas evolve. See my more recent posting (July 26) on a more specific mechanism to account for fluoresence being a feature of HIGH temperature pyrolysis, i.e. of cellulose.
It’s to do with formation of benzene-like aromatic ring structures with delocalised systems of pi-electrons. (Why didn’t I think of it sooner, apart from galloping senescence that is… ? )
FINAL UPDATE: here’s an in-depth analysis of the fluorescence problem that I received yesterday from Adrie in the Netherlands as a comment. It’ll take me a little while to get my mind round the numerous factors
he (oops) she lists that have a bearing on what one might or might not see, so I’ll postpone from making any comments here until I’ve had more time to ponder.
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.
POLISHED STARCH-MADDER COATING
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)).”
Colin 14th November 2012