I’m sorry that we never met, and that, since your passing in 2005, we won’t be going to, in this world at least. Nevertheless, since I have been studying your paper in Thermochimica Acta on the Shroud of Turin and found it a little confusing, I hope you won’t mind my publicising some of my queries, in the hope that perhaps somebody who knows more about your work will be able to clarify it for me.
I’m referring, of course, to ‘Studies on the Radiocarbon Sample from the Shroud of Turin,’ which was published in the journal of which you were a founder and principal editor until your retirement in 1988, Thermochimica Acta. In the Abstract, you focus on “the technology used to produce the cloth, its chemical composition, and the lack of vanillin in its lignin,” as factors supporting a greater antiquity for the Shroud than the medieval date suggested by the radiocarbon dating tests of 1988. I hope I may be able to examine these claims in detail, as I believe they do no such thing.
Your paper begins with the statement that Professor Gilbert Raes had “found that one part of his sample contained cotton, but the part on the other side of a seam did not.” This is a little simplistic, if I may say so. The cotton fibres identified by Raes were indeed all on the larger of the two pieces he examined, but there were very few even there, and the other piece was so small it cannot be supposed that just because no cotton was observed, there wasn’t any. Similarly, identifying it as Gossypium herbaceum does not pin the cloth to the first century, although, paradoxically, it does suggest a pre-1500 source. Medieval European cotton was also Gossypium herbaceum. The other two common species, G. barbadense and G. hirsutum (of which, most probably, the gloves of the STuRP team were made) are American in origin. The fact that hardly any of the cotton is G. hirsutum shows that it is not modern surface contamination.
While on the subject of cotton, a little further on you say that the “main part of the Shroud” does not contain cotton. I wonder how you know? Those who studied the sticky tape samples all said they had seen cotton fibres along with the linen ones, and Pierluigi Baima Bollone, in a paper dated January 2020 (‘Quaranta Anni dopo gli Esami Scientifici sulla Sindone del 1978,’ Giornale della Accademia di Medicina di Torino), says that the twelve threads he extracted from the main part of the Shroud in 1978 contained about 2% cotton. It is true that some threads from the Raes sample contained a higher percentage of cotton, up to “>60%” according to Giulio Fanti, and cotton does seem to be unevenly distributed around the Shroud. Baima Bollone found that the proportion of cotton fibres to linen fibres in the mini-vacuum samples from between the Shroud and the backing cloth taken by Riggi di Numana was much greater than in the samples taken directly from the Shroud itself. He attributed this to the greater friability of cotton. On the other hand Thibault Heimburger, analysing a Raes sample thread (R7) found “about 15% of cotton in the outer part (from 0% to 28% depending on the location studied) and about 10% of cotton in the core of the thread.” Considering that a thread consists of hundreds of tightly twisted fibres, it does not seem to be relevant whether at any given point the cotton is on the outside or the inside of the thread. However, Heimburger’s point is that this particular thread was clearly an intentional blend, while others with a smaller cotton content could have picked it up adventitiously from the environment of the spinner.
Whether any conclusions can be drawn from any of this is hard to say. Gilbert Raes himself suggested embedding a thread in microscopist’s wax and studying a transverse section. The different profiles of cotton and linen fibres would be easy to spot and count. It seems that John Brown did something like that, as his SEM micrographs suggest (‘Microscopical Investigation of Selected Raes Threads From the Shroud of Turin,’ 2005, at shroud.com), but he did not quantify the fibres at all, although his images seem to show at least one of each.
Moving on to your ideas about dating, you begin by rejecting colour and ‘radiation defects’ as good indicators of age, which I quite agree with, and then more on to lignin, which I’m afraid I find more contentious and, I’m sorry to say, poorly referenced. Your statement: “The lignin at growth nodes on the shroud’s flax fibers (Fig. 1) did not give the usual chemical spot test for lignin (i.e., the phloroglucinol/HCl test for vanillin). The Holland cloth and other medieval linens gave a clear test,” confuses me. John Heller and Alan Adler (‘A Chemical Investigation of the Shroud of Turin,’ 1981, Canadian Society of Forensic Scientists Journal) said they tested all their samples for lignin, using the test you describe, phloroglucinol/HCl, and found none, even on the Holland cloth, specifically on sample 4F, described as “backing cloth exposed on front corner,” which is exactly the part near the radiocarbon sample. Did you carry out a test on Holland cloth fibres yourself? You don’t say so. Similarly, you do not specify the “other medieval linens” you claim to know about. Which linens were they, and who tested them? In the same paragraph you say that: “The lignin on shroud samples and on samples from the Dead Sea scrolls does not give the test.” What is your reference for the Dead Sea Scrolls? Theodore Kleinert (‘Ageing of Cellulose: Pt. VI. Natural Ageing of Linen over Long Periods of Time,’ 1972, Holzforschung) examined two ancient linens, from 2000 BC and 1500 BC, and found that the ancient linen contained “no significant difference” in lignin content between them and modern linen. Although the phloroglucinol/HCl test is quite sensitive, linen only contains about 2% lignin, which may be difficult to detect with accuracy. You can see, I hope, why I need better evidence before accepting your statement without qualification.
Given the fact that some linen from three or four thousand years ago still retains most of its lignin, your derivation of a formula demonstrating that at 25°C a sample of linen would “lose a conservative 95% of its vanillin” in 1319 year is called into question. For this, you mention some research carried out by Stanley T. Kosiewicz of Los Alamos, over two years. It is a great pity that this research is not published, nor even mentioned, anywhere else, and that you yourself do not describe it in any detail.
All you do is quote a “rate constant k,” which is 3.7 x 10^11 x e^(-123800/8.314 T), where T is the temperature in Kelvins. The time for a particular proportion of lignin to remain after decay is given by: − ln(1 − α) = kt, or, to rearrange the equation, t = -log(1-α)/k, where α is the “fraction reacted at any time.”
From this, you say that: “If the shroud had been stored at a constant 25°C, it would have taken about 1319 years to lose a conservative 95% of its vanillin. At 23°C, it would have taken about 1845 years. At 20°C, it would take about 3095 years.
My calculations differ slightly.
If α is 0.95, and T is 25°C or 298.15 K, then k is 3.7 x 10^11 x e^(-123800/8.314 x 298.15),
and t is -(log(1-0.95) / ((3.7 x 10^11 e ^(-123800/8.314 x 298.15))), which is 40667506725 seconds, or about 1260 years.
If T is 23°C, then the time is about 1760 years, and If T is 20°C, then the time is about 2950 years.
Since, as you know, the Shroud was in a fire so hot that, according to legend, molten silver (melting point 962°C), it is a little surprising that you do not apply hotter temperatures to your formula, instead claiming that because of linen’s low conductivity, most of the Shroud would not have got very hot anyway. I’m afraid I don’t agree. Heat transfer through folded cloth is as much through the interstitial air as the material itself, and involves radiation and convection more than conduction.
If T is 300°C, then the time is about five minutes.
So by your own criteria, the Shroud could not be expected to contain lignin, even if it were medieval. However, Heller and Adler found no lignin in the Holland cloth or the patches either. I suspect this to be due to the unreliability of the phloroglucinol/HCl test when used on individual fibres. In fact, it is more likely that there was, and still is, lignin throughout the Shroud.
Next you address a coating of medieval paint on the radiocarbon corner, finding madder red, combined with a gum and a mordant, coating the fibres. This I find not unlikely, but I will take issue, if I may, with your determined announcement that this is not found on the Holland cloth. I believe it is. The Holland cloth is very discoloured in areas not covered by the Shroud, as can be seen by the brightness of the area under the Raes sample now exposed. I don’t think this can be due to oxidation – the area under the Shroud has the same atmosphere as the area exposed – or to light. After all, the Holland cloth is a couple of hundred years more recent than the Shroud, but has darkened considerably more. And, of course, the whole thing has only very rarely been exposed to any light at all. The (to my mind) rather fanciful suggestion that a minute area of repair was carefully painted to match the rest of the Shroud should be enlarged to suggest that the large areas of bright white Holland cloth were deliberately darkened to match the rest of the Shroud, and that some of the stain was smeared onto the Shroud itself.
However, although I find your observations of this substance compelling, I can’t agree that the radiocarbon date of the area is seriously compromised by it. You note how easily it is washed off, and it is not possible that the cleaning regime of the three laboratories, which involved at least three washings, did not substantially remove it. It’s is not impossible, though, that any traces that remained were responsible for the slight chronological gradient along the length of the sample strip.
Moving on, your next topic is the mass spectroscopy of various threads, and an attempt to demonstrate that the radiocarbon sample was different from the rest of the Shroud. To illustrate this you give two images, here arranged so that their axes are similar, and annotated by me.
In your Thermochimica Acta paper you say that the top image demonstrates the decomposition of hydroxymethylfurfural into plain furfural at high temperatures, which is typical of cellulose pyrolysis, while the lower image demonstrates the production of furfural without the intermediate stage of hydroxymethylfurfural, at low temperatures, which is a feature of pentosans, such as a “plant gum.”
So far, so good, but the two graphs are not necessarily incompatible with the same material. It is a pity that you do not show an ‘Image Fibre’ graph from the same temperature as the ‘Raes Sample’ one. Presumably it would show no hydroxymethylfurfural – just like the Raes Sample one – but also, if you are correct about the pentosans, no furfural either. But without being able to compare the two, we cannot see for ourselves, although there were, you say, “dozens of pyrolysis/ms data sets” available. Also, in a companion paper, ‘Pyrolysis/Mass Spectrometry Applied to the Shroud of Turin,’ 2004, at shroud.com, you show the upper graph, this time labelled “Mass spectrum obtained from a low-temperature pyrolysis of Shroud image sample 1EB,” complete with its hydroxymethylfurfural and furfural, in spite of claiming in your Thermochimica Acta paper that this only occurs at “about 240°C.” These two papers are contradictory. I wish you could explain that.
Furthermore, you also mention, almost in passing, that the huge spike at mass 131 on the Image Fibre graph is indicative of hydroxyproline, “a pyrolysis product of animal proteins.” You say that this is a feature of “apparent blood spots,” which makes us think that the Image Fibre graph is from a blood-stained one, although you do not say so. You also do not say whether the rather smaller spike on the Raes Sample graph is also derived from animal protein. In your shroud.com paper, you state specifically that the Shroud Image fibre came from Sticky Tape Slide 1EB, and that 1EB (from the calf of a dorsal leg) is not associated with blood. In your posthumous book, ‘A Chemist’s Perspective on the Shroud of Turin,’ (2008, at shroud.com), you explain that peaks of mass 131 which are not associated with blood do nevertheless appear at “much higher temperatures,” this time associated with the decomposition of cellulose, but this conflicts with your identification of the graph as “low temperature.”
To be honest, publishing these two graphs alone without a proper analysis of them does not fill me with confidence in your argument. What are the peaks at mass 169 and 181 in the Image Fibre graph, and would they have been present in the Raes Sample graph if it had been extended that far? What is the significance of the distinct but decreasing peaks at 56, 69, 83 and 97 on the Raes Sample graph? You will know that Marco Bella and associates have shown that “long aliphatic chains” (they give hexadecan-1-ol as an example) produce spectra with similar descending peaks, such as (for their example) at 55, 69, 83, 97, 111 and 125. If the very similar sequence in your Raes sample is indicative of such a chain, it shows that a hydrocarbon contaminant is present, with or without any pentosans. In fact Bella et al. also point to the sequence 54, 68, 82, 96, 110, 124 as also possibly due to an aliphatic chain, eliminating the evidence for furfural altogether.
Sadly it will take another chemist as experienced as yourself in thermochemistry to resolve these difficulties, which may not happen any time soon. It is a pity that you give no references at all for your description of the pyrolysis products of cellulose at high or low temperatures, which would enable me to check for myself.
You will, I’m sure, know that your Thermochimica Acta paper is invariably trumpeted as the single most powerful counter to the confidence of the Nature report’s conclusion regarding the date of the Shroud. With that in mind, I’m sure you’ll agree that it is a pity that peer-review did not flag up some of the concerns I have raised here.
Best wishes,
Hugh