Friday, October 24, 2014

Modelling the Shroud of Turin image with a flour-assisted Maillard browning reaction.

The experiments I'm about to describe may turn out to be the most important of the scores I have done and reported here and elsewhere. There again, they may turn out to be totally irrelevant (it will probably need a STURP Mk2, courtesy of the Vatican and Turin custodians). But experimental modelling of the TS image has been my niche interest and activity, so to speak, making it important to get this posting not just scientifically-respectable, but readable and comprehensible to all visitors, whatever their level of scientific literacy. In other words, I'm going to keep this as simple as possible, albeit at the risk of it seeming light. For all I know, it is light, and must leave others to judge.

 Here's a summary of the experimental design.

Fig.1: Sprinkle plain white flour onto linen from a 'pepper pot' next to a straight edge.

Yes, that's ordinary plain white flour that's been sprinkled onto the linen, The purpose of the rule is to get a abrupt edge to the flour, across which a heated metal template will then be placed to produce a scorch imprint that is (a) with flour (b) without flour (control). One can just see the end of a brush in this cropped picture that will be used to spread the flour as evenly as possible.

Fig.2. Appearance after smoothing out the flour (with added contrast/brightness to highlight the flour).

Fig.3. Remove the straight edge. Now ready for the first imprinting, where a heated metal template will be applied so as to make contact with flour/non-flour zones simultaneously.

Fig.4. Heat up  metal templates on a ceramic hob (two near-identical aluminium sharpeners were used, labelled A and B for my own convenience).

Fig.5: Success! The flour greatly assists thermal imprinting of an image of the template. (Some distracting images from a previous experiment have been masked).

Fig 6:  The same experiment as above, but repeated 4 times. The template was applied twice in the first two pressings (labelled 1 and 2 above) and three times in the third and fourth pressing. Note again how the first pressing abstracts so much heat from the template as to render it less capable of producing a second or third imprint.

 Conclusion. The white flour performed exactly as predicted (see earlier, and BELOW)  making it possible to create a scorch imprint on linen at a lower temperature  than  needed to scorch uncoated linen.

 Why was the above result predicted? Here's a brief recap of the thinking that led to my doing what otherwise looks more like kitchen cookery than scientific experimentation.(One of my closest and dearest relations made little attempt to conceal displeasure at the perceived 'downmarket' direction this project had taken, coinciding with the appearance of McDougall's Plain White Flour!).

Yes. I'm pausing here to explain the background thinking that lead to the above experiment. There are more experiments to come - indeed in this same posting - but first I need to make sure that folk are aware of the rationale for the present series of experiments before ploughing on.


It began many moons ago (Spring 2012 to be precise) with the hunch that the reported properties of the TS scorch fitted closely with those of a contact scorch, at least at the macroscopic level. Sure, there are unresolved questions about microscopic properties, but as I recently said elsewhere, I'm far from convinced that the so-called microscopic properties are real and/or significant if based, as appears to be the case, on nothing more than photomicrographs of TS fibre bundles, notably the (excellent) Mark Evans pictures, finally released from STERA's copyrighted image bank thanks to Thibault Heimburger MD).

It's one thing to say it's a scorch. But why would a medieval forger opt for that technology, given it requires an initial investment of time - and money- to get things right. Why not simply paint an image, as proposed by Charles Freeman?

Answer (speculative needless to say)?

The aim of the forger was to create an image that could be claimed to be have been left by the crucified Jesus immediately on being transferred from cross to Joseph of Arimathea's "fine" linen. It would have been an image imprinted in blood (obviously), but, less obviously in sweat as well. But from the very beginning of its recorded history, the TS image has been referred to as "sindone" (Latin) or suaire (French) which has connotations with sweat and sweat cloths (as in the Veronica Veil)..

So a medieval forger may have been looking for a means of simulating a "faux" sweat imprint. What's more, it would ideally need to be novel and sophisticated technology that would not be immediately be spotted as "old" technology and  instantly dismissed. In other words, there had to be an exotic, state-of-the-art aspect to the technology that would intrigue the first cohorts of relic-seeking pilgrims.

So what may have been exotic new technology in the 13th/14th century where making images are concerned?  That was the question this blogger was asking himself nigh on 3 years ago, and it did not take long to think of an answer (admittedly not terribly original or earthshaking) - namely INVISIBLE INK.  

I used to have a hobby book as a child, with a page devoted to invisible ink. One dipped a pen in either milk or lemon juice, and wrote a message on paper. One left the "ink" to dry to a near-invisible state. One then held the paper over a source of heat, and gradually the writing appeared, more brown than black, but aesthetics were not the object. All that mattered was that one could send and receive invisible messages that could be made visible merely by holding over a candle (1950s advice, now censored by H&S) or something that required no naked flame (a cooker bob etc).

Might linen, impregnated with lemon juice (maybe more hygienic than milk) serve as a better surface for imprinting from a heated template than plain untreated linen?

Result (October 2012) : a posting onto my specialist Shroud site entitled: "Refining a model: children's invisible writing trick with lemon juice allows thermal imprinting at a much reduced temperature."

It's one thing to propose a substance, available in medieval times, that might account for the TS image. One then has to define its chemical action with a view to matching up against the fine details of image characteristics. How might the lemon juice or similar have acted? Surface chemistry on the linen fibres, leaving the latter unchanged? Or some kind of chemical etching effect on the linen fibres?

It was at that point the project foundered. The literature on the 'invisible ink' effect was vague, with some claiming etching. others that no linen was required for production of dark pigments on cooling. I confirmed the latter by heating on glass.

Chemistry? Citric acid? Maybe some help from sugars too, notably the chemically-reactive ones like glucose?  Roadblock: I tested citric acid and glucose, singly and in combination, and observed no  acceleration of 'scorching' comparable to the one seen with lemon juice. There was also some unflattering comment on about qualitative, non-quantitative experimentation (shrugged off,  but no positive incentive to probe and report on unexplored areas when one's scientific modus operandi  is called into question. Needless to say, qualitative experimentation has a vital role to play, as does quantitative, the two being complementary.).

Later, much later (years not months) there was a discussion about some kind of priming of linen and I reminded folk of the lemon juice finding. Someone expressed an interest. That was the cue go googling to see if I had missed anything re the mechanism of the effect. This time I turned up trumps. There was an account in a book of the non-enzymic browning of lemon juice, i.e.a Maillard reaction. While citric acid assisted, the chemistry depended mainly on the presence of ascorbic acid (Vitamin C).

Quote from the above passage: "It seems probable that threose is a major facor in Maillard reactions involving ascorbic acid".

So what is threose? It's something this biochemist has encountered rarely. It's a simple monosaccharide sugar that resembles glucose in its chemical structure, having a potential aldehyde group that endows it with reducing properties, but has only 4 carbon atoms instead of 6. It's a tetrose, not hexose sugar.

Threose (D form - the L form from L-ascorbic acid is the mirror image). It exists in solution as an equilibrium between the open chain form (left) and the cyclized form (right). Note the terminal aldehyde (CHO) group which confers reducing properties and ability to produce Maillard reactions.

Threose reacts with free amino groups wherever it finds them to give a complex series of condensation and dehydration reactions that ends in polymerization to brown end products collectively known as Maillard products or melanoidins.

Enough of the detailed chemistry. Who would have thought that the intense scorches formed above with lemon-juice treated linen were Maillard reaction products (probably), not pyrolysed carbohydrates of linen, the latter involving carbohydrates only, sometimes oxygen, but no requirement for nitrogen.

It was then that inspiration struck. If one could sensitize linen to scorching by impregnating with the TWO component needed for a Maillard reaction - reducing sugar and amino groups - then why restrict the choice to liquid solutions (messy). Might one use a solid - especially one that was finely powdered, and one moreover that was easily available in medieval times?  Would WHITE FLOUR work?

Answer- YES!!!

What's especially interesting is that up till now, Maillard reactions have featured prominently in 'shroudie' thinking, due to the 'diffusion' model of STURP's Raymond N.Rogers.Based on microscopy of TS image fibres stripped off with his Mylar adhesive tape, he had claimed that the image resided on an impurity coating, not the linen fibres per se. The coating? He claimed, with scarcely any solid analytical evidence, that the linen had been coated back in Roman times with a layer of starch and/or soap-like plant saponins. He postulated that these polysaccharides had degraded spontaneously to reducing sugar, that then reacted with gaseous putrefaction amines  (putrescine, cadaverine, ammonia etc released by a decomposing corpse. the pros and cons of that hypothesis can be discussed another day (suffice it to say I personally cannot take the idea seriously, given the host of factors that would need simultaneously to be right, quite apart from unfavourable thermodynamics at ordinary environmental temperatures). But note the similarity (and differences) between Rogers' proposals and the one here. Rogers envisaged a starch coating that depended on the corpse to supply the amine needed for a Maillard reaction and a yellow or brown image, and a reaction at environmental temperature. Mine depends on applying a coating of flour (starch  and some pre-formed natural reducing sugars - glucose, maltose etc- AND proteins), which is heated by an applied meta template. The reducing sugars react with free amino groups present in side chains on the protein, notable the epsilon amino acids of lysine residues to form Maillard products.

Let's suppose that one has almost serendipitously stumbled on the principle by which the ghostly superficial looking Shroud image was engineered - intended to be seen as a sweat imprint. How would that Maillard reaction have been used in practice to produce an image from a template? What was the template - a metal effigy as assumed so far-  or might the technology have been adapted so as use a real person, living or dead, as the template?

What follows now is a brief description of follow-up experiments that were a little more adventurous, a little more ambitious, some might say over-ambitious (but they needed to be tried).

If the TS image had been 'faked' using a Maillard reaction in an applied coating, whether flour or something else, did it need to use a metal statue, or similar, which let's face it requires a sizeable investment of time and money. Might it have been possible to use the same chemistry but with a different technology such that no statue was needed. Indeed, thinking of Garlaschelli's powder "frottage" which used a real human being (student volunteer) might the same be possible using Maillard chemistry?

Why not indeed? Why not a two stage procedure, modelled in what follows, in which a metal template (which could be replaced later with one's hand) is first coated with a film of vegetable oil, then white flour (which should stick to the oil), and then pressed into linen to create a flour imprint. What happens if the imprinted linen is then baked in an oven with careful temperature control. Might the imprinted area be selectively scorched?

Let's start with a bas relief as template (while imagining it to be a 3D statue or even person):

All ready to go: brass template, olive oil, and a sealable polythene bag with plain white flour. First smear a thin film of oil onto the template, then place inside bag, then, gripping the edges of template with fingers (through the plastic) ensure it becomes evenly dusted with flour.

Flour-coated template, ready for first printing-by-contact

OK, not the most sophisticated way of heating the linen and its (faint) flour imprint, but I needed to have everything open for maintaining a second-by-second watch with camera ready.
Interesting! Shame about the grid (and I should maybe have knocked off that surplus flour that's left dark clumps of scorched flour and/or oil  here and there).
It's been over-roasted, obviously. That apart,  if  you look carefully, you can even see the template lettering. Shame it's reversed, as happens with contact printing.

So it's feasible in principle to create an imprint off a cold, unheated bas relief template, using the two step procedure above. But the roasting step could require very careful temperature control so as to get optimal differentiation between image and background. A little browning of the latter is not a disadvantage. Indeed Garlaschelli used oven-heating specifically to achieve a more aged look.

Now let's see how well the flour/Maillard system works with a fully 3D template.

For that, I used the brass crucifix (above) purchased off a stall in Antibes' open-air market in the Place Nationale.

First, here's a reminder of what one sees when the crucifix is heated and pressed into plain linen, no flour.

Crucifix smeared with oil, then coated with flour, as described earlier

Here's the flour/oil imprint before roasting.

Oh dear. Could do better. Like using gentle heat, over a longer period of time. Notice to fellow blogmeisters. Please do not display this photo as representative of the new technique. The only reason for displaying it now is archival: it  shows what can go wrong when one's in a hurry, using a modern electric hob with excessive rate of temperature rise. What's needed now is use of an oven with more stable temperature environment, albeit less handy for keeping tabs on progress and taking photographs.

Supplementary experiments (of secondary importance - for specialists only)

One would predict that plain starch, free of protein, would fail to give the thermal sensitization seen with white flour. The closest I could find in the local shops to plain starch was maize corn starch (misleadingly called maize flour in the UK, but clearly a washed starch, given the low protein analysis on the pack).

Corn starch spread evenly against straight edge as above

First test:  ????
At first glance, it looks embarrassing for the Maillard hypothesis. Maybe it is. Why is there such a big contrast between starch v control on the first impression, if protein is needed, which starch lacks?  But note the way the difference between starch v control falls off rapidly with the second, third and fourth imprint from the cooling template. Maybe it's only at the highest temperature that the starch pyrolyses with no need for protein, no need for a Maillard reaction.  (The grey coloration from the later pressings is due to water coming through from the underlay - evidence that I was pressing hard in an attempt to elicit an imprint).

Second test: ????

This a repeat of the above, with a re-heated template, see 5th image, but showing the same rapid fall-off (6th and 7th).

Reminder to self:  Forget about untreated linen controls for now: do an edge-to-edge comparison of wheat flour versus corn starch. Prediction: the first will always scorch more intensely at any given temperature than the second. Working hypothesis: Maillard reactions  to give browning occur at lower temperature than pyrolysis of linen carbohydrates.


There were two other secondary issues that needed to be addressed:

1. Was the flour-assisted image entirely on the flour, or did it imprint on the linen as well. If the former, would it wash off?

2.   Is the oil entirely necessary to stick flour to template? Can the oil be dispensed with?

Dealing briefly with the first: "How firmly is that 'toasted flour' attached to the cloth? All I can say for now is that some test strips were placed in (a) tap water and (b) soapy water overnight, and had not noticeably dissolved in either liquid.

Update: the same was true two weeks later. The flour-assisted image is firmly attached to the linen. Quite how is a matter for speculation.

Stopped here 07:50, 19Jan 2015. More to come later today.  Ignore what follows.

Might this simple technology have been used by a medieval artisan as the chemical basis for producing the image on the Turin Shroud? Answering that question may involve a great deal of further experimentation (on the TS as well as in model systems), but as the man said: "The longest journey begins with a single step".

Next question: how easy or how difficult is it to adapt the above technology for producing a negative imprint on linen (recalling that the TS image shows light/dark reversal as first shown by Secondo Pia in 1898)? Does the linen itself have to be pre-coated, or can one attach the flour directly to a template? The latter note does NOT have to be heated. Maybe the coated linen can be heated after imprinting first with flour. I shall continue for now to deploy a metal template (unheated), but note that there is no longer any reason for using metal. Any object with  a modicum of 3D surface relief could be used to leave its negative imprint on linen, at least in principle - including, dare one suggest, a cooperative human volunteer, as in those magnificent Garlaschelli studies.

To keep things simple (initially) a  shallow bas relief  horse brass was deployed in the next experiment (but one could imagine it being a live human being as well, assuming he or she were willing to submit to the messy  but otherwise low-biohazard procedure about to be described).

Update Saturday pm

Have just used a fan oven set at 240 degrees Celsius and obtained this result with the new 'flour fingerprint' technology.

It's an acceptable image in gross terms, would you not agree? There's just one snag. It was powdery and easily brushed off. So there's a difference between roasting over a hot plate and roasting in a fan oven. Why that should be is something that is not immediately obvious. Or maybe there was some other difference, e.g. in amount of vegetable oil. Either way, it's good to see an image which (though I say it myself) might be said to occupy the Goldilocks zone (neither too sharp, nor too fuzzy). There is still so much to do. Maybe I should advertise for a lab technician, one who is prepared to evacuate the 'laboratory' whenever the General Manageress makes her entrance some 3 times per day.

PS:  It was even possible to get a second imprint off the same horse brass without needing to recoat with oil and flour, though the quality was needless to say somewhat inferior (and still brushed off).

It's only mentioned here since it demonstrates what might be termed the robustness of the imprinting technology.


The image from that crucifix, obtained with a Maillard reaction that did NOT require pressing hot metal into linen, was a bit disappointing, but then it was the first trial of the new technology. A better result was obtained using a bas-relief metal template, i.e. a horse brass with King George VI.

This is simply to flag up the new direction my research has taken, prompted by the discovery that the Shroud image is in fact two-tone (see posting that immediately precedes this one). While speculative, it is possible that the image is a composite of an intense  orange-brown scorch on linen fibres per se, with a wider more diffuse image that represents something else, possibly a Maillard product on something that had been added to the linen as a surface coating.
Takeaway message: the initial hunch was confirmed, namely that flour does indeed contain all the ingredients for an in situ Maillard browning reaction:  flour dusted onto the surface fibres of linen should, and indeed does, act as a heat-sensitizing agent. The beauty of flour, needless to say,  being a finely particulate solid, is that it does not soak through as would a solution to the opposite side to give an image there as well, except possibly a ghost image due to migration of a few particles through the interstices of the weave. ( See "Shroud second face". Possible explanation?)


Hugh Farey said...

Hi Colin!
Half-term arrives, and I have dissolved some dextrin and boiled up some saponaria. Next I'll soak some linen in both, individually and mixed, and tomorrow...
unfreeze my baby rats. The lab will no doubt stink of rotting flesh after a while, but surely, the Lord not allowing his son to know corruption and all that, I won't have to endure it too long.
Some months (years?) ago, I formulated the "soapy custard" hypothesis. Could this be it?
If there's no joy with the rotting rats, or when its safe to go back in the lab, I'll try heating it as well.
Ooh! What fun...

sciencebod said...

Nice to hear from you Hugh. Good luck with your experiments.

You wouldn't happen to know would you whether or not melanoidins fluoresce under uv? Did Ray Rogers ever ask that question I wonder?

Hugh Farey said...

Melanoidins, eh? Well, toast fluoresces quite nicely, whereas bread does not. And scones do too (I didn't test uncooked ones!). Both dextrin and cornflour are pretty fluorescent even unheated, and do not appear to change when cooked. Tonight I will wander around the kitchen with a UV light and watch some cooking!

sciencebod said...

Now you've got me confused Hugh. I thought you no longer had any time for a contact scorch mechanisms due to the fluorescence that accompanies it (the TS image being famously non-fluorescent). So why are you attempting to demonstrate a Rogers' type coloration, given it's supposed to be a Maillard product, and given the examples you list of toasting and other Maillard products being fluorescent?

Hugh Farey said...

I like to keep an open mind, and you did ask about melanoidins. And I can't do much in my lab as the rats are just begining to reek! I hope this experiment will be done with before the children come back after half-term...

sciencebod said...

Don't get me wrong Hugh. Keeping an open mind is most credit worthy. What I don't understand is why you closed your mind a while ago on the 'scorch hypothesis', citing fluorescence as you chief objection, but are prepared to keep an open mind on a Rogers' type mechanism when melanoidins, i.e. brown Maillard reaction products, are also fluorescent?

Or am I missing something here? Are you operating on the assumption that melanoidins formed at low temperature differ from those formed in toasting, baking etc.

Incidentally, there was a reference today to a posting that Thibault did in 2012 in response to one of mine, saying that melanoidins could form at moderate temperatures. My claim that the rates below 50 degrees or thereabouts were small in a glucose/casein model system were countered by his unearthing data saying that glucose performed poorly compared with pentosan sugars such as arabinose and xylose. But where do they come from? There would be scarcely any in Rogers' hypothetical "starch fractions" except as minute impurities in crude starch. Was he thinking that Rogers' 'saponins' provided them? Am I not correct in thinking that no one has ever detected saponins on the TS - that like the "1st century starch" they are a purely hypothetical entity?

I see that Ray Rogers has been described as a 'chemical kineticist'. That's the trouble if you ask me, given that some reactions are under thermodynamic, not kinetic control (see wiki entry).

I strongly suspect that to be case for Maillard reactions up to 50 degrees or so, judging by the huge response in relative terms to each extra degree Celsius. Suddenly the penny dropped. Rogers was focused for most of his career on the stability of high explosives in storage. The decomposition of explosives is NEVER under thermodynamic control. They wouldn't be explosives were that the case. Would it be unkind to say that Rogers gradually acquired a blind spot for chemical reactions that are under thermodynamic control?

sciencebod said...

PS Have just unearthed this Dutch paper.

It's not an easy read, but the message seems to be: "Don't forget thermodynamics when considering rates AND yields of Maillard reactions in food."