It’s amazing, is it not, that despite the Shroud having been the subject of intensive study over several decades, albeit with limited samples, we still don’t have any real substantial information as to the nature of the image? At least the STURP team, to give it credit, said there was a resemblance with a scorch, based on spectral reflectance and absorbance measurements, that it was chemically bleachable with diimide, suggesting the colour is due to reducible double bonds. Thus the hypothesis that the image is due to chemically-dehydrated constituents of linen, MAYBE the intrinsic carbohydrates, or MAYBE extrinsic ones like acquired starch or reducing sugar… but there’s no escaping that M word…
It is this ignorance that has allowed a particular theory to gain traction, namely Raymond N. Rogers’ Maillard reaction. It’s one this blogger is more inclined to call Rogers’ “Definitely Not a Scorch” theory or “Desperately Seeking an Alternative to a Scorch” theory.
Leaving aside my own profound scepticism, it says that the image is the result of a chemical browning reaction between one or more putrefaction amines released by a recently deceased corpse and chemically-reactive reducing sugars acquired by the Shroud linen in the course of manufacture. Ammonia, cadaverine and putrescine are conjectured to supply the amines, while “starch fragments” and “saponin-containing soapwort” are allegedly prime candidates for supplying the requisite reducing sugars. Yet the Shroud image is said not to contain excess nitrogen over non-image areas: while one encounters claims for the presence of starch or starch fragments on the Shroud, there are no claims that I am aware of for the presence of reducing sugars like glucose, maltose etc (starch itself being essentially non-reducing unless extensively degraded to simple mono, di,- tri saccharides etc with free aldehydic functions).
OK, let’s now cut to the chase. Why is so little known?
The easiest answer is that there is only one Shroud, highly revered by those who believe it to be the actual burial Shroud of the Son of God. The Shroud’s custodians, ever mindful of their responsibilities, are simply unwilling to allow the kind of extensive sampling and testing that would leave bits missing, especially on image areas (bearing in mind that the radiocarbon dating was done on a non-image portion from an inconspicuous corner).
There are two responses to that. One I’ve come across recently is the use of state-of-the art scanning techniques that are allegedly non-destructive. They go under a variety of initials and sound very impressive. But it’s not clear what these surface probes are measuring relevant to the Shroud. OK, one may get a map of surface contours, maybe accompanied by some indication of chemical signatures, but can it answer the question as to how the image was formed? Personally, I doubt it, unless it were authenticated in a range of model systems. Ah, but that is the crux of the problem. What is or is not a relevant model system when one does not know the means by which the image was formed? One is in a chicken and egg situation.
Personally, I think it is time to cut the Gordian knot on the nature of the Turin Shroud image. Failure is not an option for science, and it leaves the field exposed to pseudo-science.
What one cannot do is assume that any new tests would be so destructive to the fabric of the Shroud as to make it a waste of time to develop them. One develops the test, and then attempts to scale it down, such that permission might be granted for some image area to be sampled, say from the less photogenic dorsal image.
Secondly, there is no escaping the need for a model system or systems on which to develop analytical techniques. Top of my list would be a thermal imprint, aka scorch. I don’t just say that just because I am firmly of the belief that the Shroud is medieval, and was produced as a scorch. I say it because there is no other explanation that I am aware of that explains crucial aspects of the Shroud image as does a scorch. I refer to the negative (light/dark reversed image) that is dramatically improved by another light/dark reversal. As such, techniques should be developed with model scorches if only to FALSIFY, or attempt to falsify, the notion, misguided or otherwise, of the Shroud image being a simple scorch. Proving what something is NOT is often the way that science proceeds, rather than going for gold and proving -, or hoping to prove, assuming that were possible- what it is.
So for the rest of this posting I shall outline a protocol that I consider could be usefully adopted, one that places the thermal imprint (scorch) at the head of any list of working hypotheses, and which does not shy away from good old fashioned wet chemistry with no regard initially to sample size. First things first. Develop the principle, then attempt to make the method quantitative, then attempt to scale down as far as is practicable.
Look at frontal image knee region of the Shroud.
There is a large water stain. But there is body image underneath that has not eluted. If it had it would all have desorbed and moved with advancing solvent front. That suggests that the image pigment, whatever it is, is at least strongly physically adsorbed to fabric. That in turn means that no chemical characterisation is likely to make much progress unless or until body image is physically or chemically separated from fabric. One could try a range of physical desorbing agents of varying degrees of polarity, ranging from mixtures of organic solvents, through salt solutions to agents that disrupt hydrogen bonds, e.g. like DMSO or dimethylformamide. There is a possibility that none of these would work if the image were chemically-attached to cellulose or even a substantial fragment of that polymer.
There is a strategy that no one seems to have employed yet, or maybe even considered, which is to start by dissolving (more correctly, dispersing) the cellulose. (Cellulose chains are too long to be brought into true solution).
Yup, “dissolve” away the intact cellulose, as well as any cellulose that is in varying degrees of denaturation, while monitoring the yellow or brown colour. The latter is the target chromophore of interest that may or may not be attached to cellulose, or fragments thereof, whose DP (degree of polymerisation, i.e. chain length) one can only guess at. Never mind. Simply “dissolve” the cellulose as a first step into liberating the target chromophore from the bulk of substrate, matrix, vehicle, call it what you want. At the same time there will be a concomitant liberation of other components of linen that are bound in various ways, physical or even chemical, from bulk cellulose, like the non-cellulosic components (lignin, hemicelluloses, pectins etc). It’s much easier to start a fractionation scheme with a liquid solution, or even dispersion, than with a solid substrate.
So which agent can be used for the initial dispersion?
Linen is not dissimilar from paper and even wood (the latter having a higher lignin/cellulose ratio), so one’s first thought are the processes that have been used for decades for converting cellulose to man-made, semi-synthetic rayon fibre that rely on initial solubilsation of cellulose, followed by re-precipitation, i.e. regeneration of the fibre. The two chief ones are the viscose rayon and the cuprammonium process. The first uses a combination of alkali and (smelly) carbon disulphide. The dispersion is then injected through a spinneret into acid solution – the cellulose precipitates as a thread.
Let’s ignore that first one, at least for now. Apart from the objectionable nature of the reagent, the CS2 forms complex with the dispersed cellulose, so-called cellulose-xanthate, which as the name implies is yellow. We don’t want yellow intermediates, even if the final precipitated cellulose is white. Why not? Because we are wanting to track the whereabouts of the Shroud image chromophore. Nor do we want exposure to strong alkali, since that might chemically degrade the scorch or Shroud chromophores. We want a less aggressive reagent. That leaves the cuprammonium process, which looks far more promising for starters.
The process is easily demonstrated on a small scale. There’s a graphic I’ve located online, (see top of page) though it’s not terribly good in showing the final precipitated fibre.
One either buys in copper hydroxide (or copper carbonate), dissolves it in an excess of ammonia solution (aka “ammonium hydroxide”) to get an attractive deep blue solution. The latter has the property of dissolving filter paper and other reasonably pure sources of cellulose (so one assumes that linen may work equally well, though it may benefit from de-waxing with organic solvent). The blue liquid is then injected from a syringe into dilute acid, and hey presto the cellulose re-precipitates as a white thread. (Well, blue initially, but the colour fades as the copper leaches out)
If one is really into DIY chemistry, then one can start with plain old copper sulphate solution. One adds sodium hydroxide solution, which gives a pale blue gelatinous-looking precipitate of copper hydroxide. One then filters that off, and washes it well with water to get rid of unreacted alkali etc. The precipitate is then treated as “copper hydroxide” as above to get the same end-result.
Through googling I have discovered there are more modern reagents that have also been found to have the property of dissolving cellulose. They are N-methylmorpholine-N-oxide or a mixture of lithium chloride/dimethyformamide.
There are also variants on the cuprammonium reagent that replace the ammonia with other nitrogenous copper-chelating agents, e.g. ethylenediamine, and also a chelated cadmium-reagent, but I personally have no experience with any of those.
So here’s the protocol. One begins with model scorches on linen. One disperses the linen cellulose in one’s cuprammonium reagent, or one of the alternatives. On re-precipitates the cellulose, spins it off, and then follows two pathways in parallel. The first concerns the cellulose. One measures the recovery as a percentage of the cellulose in the linen. To do that, one needs to have a robust analytical system for non-starch polysaccharides, e.g. the Englyst/Cummings procedure developed for plant cell wall fibre that removes starch initially with alpha-amylase and/or other starch digesting enzymes, then subjects what is left to hot acid to hydrolyse to individual sugars (glucose, arabinose, xylose etc) which are measured by gas-liquid chromatography. The more superficial the scorch image, the greater should be the recovery of intact cellulose. (It would be interesting to see whether a visible scorch can be obtained with 99% cellulose recovery, indicating a high degree of superficiality, and possibly a reaction with something other than linen cellulose, recalling that linen is not just cellulose. (If reacting with something other than cellulose then that might be accompanied with a reduced yield of the pentosans that are a feature of hemicelluloses rather than cellulose).
The other parallel pathway is tracking what has happened to the yellow or brown scorch chromophore. If one is lucky, it is now in the acid supernatant, separate from the re-precipitated cellulose. One could be unlucky, and find it is adsorbed onto the cellulose, and still “intractable” so to speak, but that seems improbable: physical adsorption is less probable in acidic solution, and if found there is always the option of adjusting the pH with the prospect of the chromophore desorbing under neutral or mildly alkaline conditions. (I trust you are enjoying this excursion into armchair chemistry, all you spellbound readers out there. Hello. Hello. Anybody still there?).
If one is lucky, and the chromophore is in the supernatant, or can persuaded to desorb of cellulose and go into solution, the next step is concentrate it. There are a number of possible strategies. Provided it is not too polar, it might be possible to perform a solvent extraction, e.g. using the Folch partition with chloroform/methanol/water, maybe with initial pH adjustment. It might be possible to concentrate by gel filtration or gel permeation chromatography (see this link for the difference)
Alternatively, there is the possibility of simply removing water by freeze-drying, and testing various kinds of chromatography to the solid residue, e.g. thin layer chromatography, glc, hplc etc.with or without derivatization to get more volatile derivatives. There is always the sledge hammer option, namely pyrolysis mass spectrometry (pms), where the sample is heated in a vacuum, blasted with an electron beam to reduce it to molecular fragments that can then be separated. Their individual m/e ratios can then be compared with literature values for known fragments and the parent structure deduced (much of this is now computerised).
Now here’s a possibly viable option that could be useful if or when a Shroud sample became available. Assemble a library of pms “fingerprints” from model scorches obtained under a range of conditions – especially different temperatures, inert v oxygen-containing atmospheres etc etc. even if interpretation of each spectrum in terms of precise chemical species proved difficult, the availability of those fingerprints might help decide if the Shroud image was or was not typical of a heat scorch.
There is always the possibility of a further cellulase digestion (cellulAse note – a cellulose-digesting enzyme, usually of fungal origin), but there would be some technical difficulties introduced, namely the presence of a protein (the fungal enzyme) that might interfere with the analysis of Shroud chomophore.
Throughout the entire procedure one would of course be monitoring for fluorescence. Initially it might be the yellow-green colour that Hugh Farey and others have seen in their Shroud studies. Would the colour fluorescence survive the extraction procedure? Would it be enhanced or weakened? Could the fluorescence be used as a sensitive way of tracking the chromophore from model scorches and even (perish the thought) prove to be the undoing of the scorch hypothesis (I leave others to imagine the precise details of so personally demoralising a scenario).
What one would like, ideally, at the end of the day is a unique signature at the molecular level of a “scorch”, one that can be isolated from all surrounding interferences by the reductionist procedure outlined, and then converted into a microassay procedure that can be precisely quantified. That would then be the time to go the Turin Shroud custodians and say: look, we think we know how to test for, and possibly falsify the scorch hypothesis. Can we please have a square cm or two (maybe more or less) from a less conspicuous region of the body image, say the dorsal side. On second thoughts, not square shaped, but made to look like one of those 1532 burns or so-called poker holes (where there is already substantial damage, such that new damage would not show up too much).
To summarise: use scorched linen to devise a procedure for extracting and “bottling” the scorch chromophore. Attempt to characterise and quantify the isolated chromophore using modern micro-analytical techniques. Then seek permission to try the same developed procedures on the Shroud body image chromophore. Don’t pussy foot around – dissolve the backing cellulose away from the image to see what is left.