Modelling the image of the Turin Shroud – an interrupted experiment using onion epidermis – just one cell thick.

Stop Press: updated Wed 11:00 London Time with a near CONCLUSIVE result of the interrupted experiment (having broken off to respond to Dr. Di Lazzaro, he of the excimer uv laser beam model): see below.


One criticism that I keep hearing about the hemicellulose model (see previous post) is that the reported thickness of the image zone, confined to the superficial primary cell wall (PCW)of a linen fibre, would be too small (reckoned to be 200nm) to achieve by a medieval forger.

There are a limited number of ways that I, as a retired scientist, using a kitchen as a laboratory, and without sophisticated microscopes, can hope to address that question and obtain an authoritative answer. But  for my own amusement,  if nothing else, I wondered about ways of addressing it indirectly which  might at least provide suggestive evidence for the time being.

So many folk seem to imagine that 200nm (that’s 1/5000th of a millimetre) is a microscopic distance that could only be seen under the microscope. Not so. As I have previously pointed out, it is the typical thickness of the gold leaf that medieval artisans used to illuminate manuscripts and to gild base metal.  That led me on to thinking: it is a simple matter to strip sheets of epidermal cells off the scale leaves of onions that are just a single cell thick. Why don’t I get some of those sheets, let them dry out (to model linen fibre PCWs), lay them on top of linen, and then see if it is possible to scorch those sheets of “microscopic” thickness  (presumably with fairly typical hemicellulose content) without scorching the underlying linen?

Well, no sooner had I prepared my single-cell onion skins, and put them on one side to dry, than a post appeared on a site (see side bar) to which I seem joined at the hip these days in which the very scientist who prompted my (reawakened) interest in the Shroud has attacked my ‘thermal imprint’ theory.

So I am minded to make this post serve a dual purpose – to continue with the modelling of the thermal imprint by the back door onion route, and at the same time address the objections and arguments that have been raised, since they are germane to the issue.

So this post will be by way of a work-in-progress. Here for starters is a picture of my onion skins:

The photograph was taken immediately after stripping off the epidermal layers from onion scale leaves. It has since dried out to leave fairly rigid sheets without noticeable curling or shrinkage, and is ready for experimenting with.

More to follow, including a response to Dr. Di Lazzaro (ENSA), he who uses excimer uv lasers in a heroic attempt to model the Shroud image (in contrast to my boring old pre-21st century physics and chemistry)…

Update on the experiment: first result obtained this morning. Somewhat inconclusive at this stage:

It may look at first sight as if the scorch has gone clean through the layer of onion cells into the linen, but most of what you see is adhering burnt onion skin (see slight reflection top left)much of which could be stripped off with adhesive tape

The onion epidermis scorched well (maybe too well) and there has been scorching of the linen too – or at any rate apparent scorching (hang in there Dr.Lazzaro). But looking at the “linen” scorch through a lens I get the distinct impression – also apparent in the photo) that at least some of it is scorched-on epidermis that has stuck to the linen. Consistent with that view is that fact that 3 applications of adhesive tape brought off progressively more of the image off (reminiscent of  Ray Rogers experiments?) although not all. I need to try a lower temperature, and maybe a better template (instead of a bent safety pin).

Experiment 2: For this I switched to using a replica of higher heat capacity (a light alloy pencil sharpener), which could be tested more easily on linen before applying to a sheet of dry onion epidermis. (it does not lose too much heat between each test “branding” making it easier to gauge and wait for the correct temperature.

This photograph should speak largely for itself:

The heavily-imprinted onion epidermis has been moved to take this picture, showing a virtually unscorched area between onion and pencil-sharpener template.  (See  labelled photograph immediately beneath this one).  The only scorch was  where a  protruding screw head had left an image, and one other small mark.    (It is difficult to tall if they are really scorch marks on linen, or merely scorched onion that has adhered to the linen – I suspect the latter.)         Proof that the template still had plenty of heat and scorch-potential is evident lower down, where it has been move away from where it was placed AFTER imprinting the onion epidermis, to reveal a scorch mark on the linen. A layer of plant calls – just one cell thick – can take an intense scorch with little effect on underlying linen fibres.


Afterthought: here’s the same photograph as above, with an aid to spotting the two critical regions (blue and red dashed lines)

Onion epidermis, dried, after thermal imprinting from heated metal template with underlying "linen" (cotton actually, contrary to product description). The area enclosed in blue dashed line was originally under the epidermis, and has been scarcely affected by the intense scorching of the epidermis (the latter moved aside for photography). However there was still sufficient heat in the template to scorch unprotected fabric, as shown by the area within the red dashed lines, which was a scorch produced from the same template immediately AFTER scorching the epidermis scorching,  despite cooling. That was an essential control, one that has been overlooked in some of the attempts by Shroudie nitpickers and/or ideologues to trash this crucial experiment, one that shows that a scorch image can be both highly superficial, yet short-range in its penetrative ability.

Onion epidermis, dried, after thermal imprinting from heated metal template with underlying “linen” (cotton actually, contrary to product description).
The area enclosed in blue dashed line was originally under the epidermis, and has been scarcely affected by the intense scorching of the epidermis (the latter moved aside for photography), except for the protruding screw head. However there was still sufficient heat in the template to scorch unprotected fabric, as shown by the area within the red dashed lines, which was a scorch produced from the same template immediately AFTER scorching the epidermis  despite cooling. That was an essential control, one that has been overlooked in some of the attempts by Shroudie nitpickers and/or ideologues to trash this crucial experiment, one that shows that a scorch image can be both highly superficial, yet short-range in its penetrative ability.

Late addition (5th March) – a repeat experiment, showing how there is virtually no scorching of the underlying linen when the scorched onion epidermis is peeled back. (This experiment used a damp dishcloth behind the linen which improves the imprinting of image off hot replica (more give/heat sink)

Right, let me talk you through the experiment. The pencil sharpener was heated until it began to leave a scorch mark on the linen. It was then pressed onto the dried onion epidermis (just one cell thick remember) and then withdrawn after a second or two, leaving a heavy scorch mark on the skin. But when the skin was lifted, there was almost NO scorch on the linen underneath EXCEPT for an tiny image of a protruding screw head (which had been the first to make contact with the linen).* The fact that there was still a lot of heat in the pencil sharpener became clear in two ways: first when I moved it away from the experimental zone (to bottom of picture)  it left a new scorch mark on the linen – you can see an image of the the outlines and again, that protruding screw head. Secondly I tried picking it up minutes later and had to drop it quickly – or it would have been me that was branded with the mysterious Sign of the Pencil Sharpener.

*Postscript: in fact there is possibly an exceedingly faint yellow discoloration on the linen where most of all the template made contact, although that is hardly surprising, given the immediate contact with highly-browned onion epidermis.

Sorry, Dr.Lazzaro. I made no secret of the fact that as far as I was concerned, your theory was a non-starter on  common sense grounds alone. OF COURSE one can produce a faint scorch on linen – as faint as you want, simply by adjusting the variables of temperature, time, applied force etc. But since you like hands-on experiments (snap) then here’s a result you cannot ignore.  Nope, as I said earlier, it’s only a model in which onion epidermis is being used to model the primary cell wall of flax linen, so caveats are necessary. But one CAN produce, and HAS produced,  an impressive scorch on the onion epidermis with scarcely any effect on the underlying linen, and the little there is probably represents highly-scorched epidermis from the most most prominent part of the template – that protruding screw head – that has stuck to the linen.

Geeky stuff: the character of the onion scorch is markedly different from that of the linen, probably reflecting the high concentration of sugars, proteins etc that are in onion epidermis, and thus forming caramelised products and/or Maillard reaction products far more readily than the highly ordered cellulose crystallites in the main part of flax fibres that are more stable to thermal degradation than hemicelluloses and simple sugars etc, ans even, it seems the PCW-associated hemicelluloses of linen in this experiment.  But that is a restatement of my theory (or working hypothesis, call it what you want) that the thermal stability of cellulose is so much greater than that of hemicellulose, probably for both kinetic and thermodynamic reasons, that selective scorching is possible where the more reactive of the two has a highly superficial location on linen fibres,  i.e. that external PCW layer, so would be the first layer that would be “branded” by an externally-applied  hot template (or heated-up medieval replica, possibly cast in bronze, to resemble a crucified man?).

“There’s no business like show business, there’s no business I know…”  I guess the same could be said for retired science bods showing off their hands-on experimental know-how in the kitchen, taking photographs for posterity at every step  ;-).

My earlier response to Dr.Di Lazzaro can be found beyond the “Read More”spacer.  Look especially in the Comments, and do feel free, please, to submit your own. Criticism welcome, provided it’s reasonably civil…

Afterthought: that image of the pencil sharpener on the onion epidermis shows ‘encoded 3D information’ of course when entered into my favourite (free) imaging software:


Here’s a C&P of the post in question. I’ll respond to each point as and when I have a minute, and send a synopsis to the other site unburdened with too much detail.

Colin Berry’s idea is untenable, and heat cannot produce a superficial colorationby episcopalian

After Colin Berry posted his statement about image formation, referenced here, I personally requested comments from members of the Shroud Science Group. This is Paolo Di Lazzaro’s answer to me and other SSG members who might not be expert enough in physics to understand why Colin Berry’s model (without experiments) is untenable. Now with Paolo’s kind permission those notes to SSG members are being published here:

Dear Dan and All:

I checked the idea of Colin Berry in the website you quoted.  In short, from a physics point of view, his model is untenable, especially concerning the depth of coloration. Let me explain why.

Berry wrote: “The scorching will initially be confined to those parts of the fabric that are in immediate contact with the hot metal; no air gap is permissible, since radiated heat will not scorch white linen. What is more, the scorch will be confined to the outermost fibres of the thread, because the scorch will tend remain trapped within the first-encountered fibres, rather than being able to “jump across” to adjacent fibres. Why is that? It is because the resistant cellulose cores that are unaffected are able to conduct away heat rapidly, bringing the temperature of the hot template down to below that which will induce scorching Is it realistic to suppose that cellulose fibres could conduct away heat without themselves becoming degraded? Yes. I believe it is.”

It is quite easy showing the above assumption is wrong, and it is one of the few cases where it is faster doing the experiment than to explain the theory. According with a paper quoted by Berry, the onset of pyrolysis in hemicelluloses is at about 220°C.  We have heated a 5-cents euro coin at about 230 °C in contact with a linen cloth. Just 5 seconds after the coin reached the max temperature the whole cross section of threads in contact with the coin was colored.  After15 seconds all the thickness of the cloth was colored and the round shaped image of the coin appeared on the opposite side. After checking in our Lab, we repeated this easy and small-size experiments in the RAI3 TV studios (GeoScienza) to demonstrate that heating linen cannot give a superficial coloration. See starting from the minute 16:30.

After the experimental demonstration, let’s approach the basic elementary physics that explain why the idea of Berry is untenable, and heat cannot produce a superficial coloration.

The hot metal transfers energy(heat) to the primary cell wall (pcw) of the linen fibrils by contact. From a microscopic view, transferring energy by contact means the hot (i.e. fastly moving)atoms of metal hit hemicelluloses molecules transferring momentum, thus increasing both amplitude and velocity of the motion of hemicellulose molecules around the equilibrium position (centroid). As a consequence, hemicellulose increases its temperature.

In the regions of contact between pcw and cellulosic medulla, we still have a transfer of heat by contact, like in the previous metal-pcw case. The temperature of the medulla will increase.  In the region where there is no contact (e.g.,a small air gap between pcw and medulla) we have heat transfer by irradiation.In fact, every material emits radiation having a spectrum peaked at a wavelength which depends on its temperature: the higher the temperature, the shorter the wavelength. This is the well known phenomenon of the black body emission, governed by Planck’s law, Wien’s law and so on (first year exam for students of Physics, Mathematics, Chemistry, Engineer).

As an example, at 20 °C the walls of a room emit radiation with a broad spectrum, peaked in the far infrared at about 10-micrometers wavelength. In the case of hemicelluloses at 200 °C the pcw emits infrared radiation peaked at 6,1 micrometers. In the case we are considering, the 6-micrometer wavelength will interact with the cellulose of the core of the linen fibril (medulla), exciting vibrational levels of cellulose that decay in heat thus increasing the temperature of the medulla.

In addition, a well known optics law tells us the penetration depth of the interaction between radiation and medulla cannot be smaller than the wavelength, that is, not smaller than 6 micrometers in this case. This fact alone explain why infrared radiation cannot produce a superficial coloration of fibers.

By the way, it is not possible that “the resistant cellulose cores that are unaffected are able to conduct away heat rapidly” (see above Berry’s statement) because of elementary fluid dynamic equations (a classical engineering problem), of a not convenient area/volume ratio of cylinders (elementary geometry) and because Berry assumes a exothermic pyrolysis of cellulose, that is,by definition, a runaway process, extended in time.

In summary, when heating a linen cloth by a hot metal in contact, well known physics models foresee the pyrolysis of the whole fibers and threads, and this is exactly what we observe in the experiments.

Useless to say, it is all the approach of Colin Berry to find a middle age technology able to create the Shroud image that is hopeless: just consider the half tone effect.  It could not have been made by medieval forgers because they would need a modern microscope to observe and then control their micrometric-scale coloration.

All the best


Update 13th March

A valid criticism was made on teh other site (see sidebar) that my onion epidermis experiment was lacking crucial evidence. How do we know that the template had been hot enough to scorch linen if applied directly. If not, then it would be small surprise that it failed to scorch it through a layer of onion epidermis, even if the latter were heavily scorched.

Actually, I did have at least suggestive evidence that dealt with that criticism, but it was not terribly photogenic. So I have just this minute repeated the experiment, taking care to ensure that the template was hot enough to scorch linen when applied directly. Here are two photographs from the same experimental area, taken from different angles:

See the imprint next to the label (“TEST AREA”). One can see where the template (a pencil sharpener) has scorched the linen – applied directly, and where it has scorched the epidermis more heavily. The question is: what is underneath the scorched epidermis? Has the epidermis protected the linen from scorching. We need to view from the opposite direction.

And here, viewed from the opposite side, one can see that the epidermis has indeed protected the underlying linen from all but the slightest, scarcely visible scorching. (I’ll try to get an even better picture without shadow in the crucial area).  That’s all it takes to protect against deep scorching – a sheet of plant tissue, just one cell thick. Cue a role for the PCW of flax fibres (primary cell walls).

here, with the onion epidermis peeled back, one can see the crucial comparison between protected and unprotected linen. Repeat: the protection was afforded by a single layer of cells that became heavily scorched in the process.

Test insertion of a pdf file


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.
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8 Responses to Modelling the image of the Turin Shroud – an interrupted experiment using onion epidermis – just one cell thick.

  1. colinsberry says:

    It would seem sensible to use the comments section to respond to Dr.Lazzaro, point by point. Firstly the title: “heat cannot produce a superficial coloration”.

    I could have shot that notion down in flames, even if I had no scientific background. Temperature is a CONTINUOUS VARIABLE (you can set it to any value you want). if heating to 100 degrees produces no coloration, but 300 degrees does, then what do yuou do? You try 250. If that produces coloration, then you keep reducing the temperature, first by, say, 10 degree steps, then 1 degree steps, until you get a barely perceptible coloration. Heat (more accurately temperature) has then produced a superficial coloration. Chances are that the chemical degradation scorch mark is highly superficial, affecting only a very thin layer (e.g. of cell wall dimensions, say 200nm). Getting a faint scorch is simply a matter of applying the Goldilocks principle.

    This would seem to me to be plain common sense. Light scorching is not the equivalent of lighting blue touch paper on a firework display (“all or nothing”). It is gradual, it is progressive, at least at the gross level. But having said that,an “all-or-nothing” effect would appear to operate at the level of individual fibres (of which there are some 200 per thread) in order to account for the half-tone effect, which I think is due to pyrolysis of hemicellulose being exothermic (in other words, once started, it tends to keep going until all the available, accessible “incendiary” hemicellulose used up.

  2. colinsberry says:

    “According with a paper quoted by Berry, the onset of pyrolysis in hemicelluloses is at about 220°C. We have heated a 5-cents euro coin at about 230 °C in contact with a linen cloth. Just 5 seconds after the coin reached the max temperature the whole cross section of threads in contact with the coin was colored.”

    Yes, but that was onset of pyrolysis as measured by weight loss. That is not the same as onset of pyrolysis as measured by change in light absorption (yellow coloration). the latter involves more subtle chemical change that does not involve loss of volatiles.

    Try repeating your experiment at 220, then 210, then 200 etc until you discover a cut-off point. That’s what experimentalists do – they make systematic changes in the continuous variable, exploring the entire range of interest – not plumping for one temperature just because someone said it’s the only one that matters on some entirely different yardstick. It’s yellowing for image formation that is the criterion, not weight loss).

  3. colinsberry says:

    It is not terribly edifying to have to plough one’s way through a lengthy section on radiation physics (with its unnecessary digs about degree level courses) to find at the end one has been misquoted on a major issue: “… because Berry assumes a exothermic pyrolysis of cellulose, that is, by definition, a runaway process, extended in time.”

    NO. I said that it was the pyrolysis of hemicellulose that was exothermic, that it differed in that respect from cellulose (endothermic) which was why one could get selective scorching of the hemicellulosewithout the cellulose being in the least bit affected. Maybe it was a typo on Dr.Lazzaro’s part, but looking at the references to cellulose medullas I doubt it. I think he has seriously misunderstood the essence of the hemicellulose model. Maybe it’s a language thing – his English is better than my virtually non-existent Italian, so I shall give him the benefit of the doubt, but I really see no useful purpose is served in prolonging this discussion any further.

    As far as I am concerned, Dr.Lazzaro has said nothing to change my view that the Shroud image was formed by thermal imprinting by direct contact/conduction. Any role for radiation would have been a minor one, because there is no mechanism for radiation-induced scorching in the absence of an opaque absorbing pigment. (Though having said that It is possible that the initial scorch image OR the sand bed in my model could act as IR absorbers, producing secondary heating effects, as discussed previously elsewhere as a possible mechanism for formation, say, of that fainter image of the face on the reverse side of the fabric).

  4. colinsberry says:

    Here is a comment I submitted to the other site (see sidebar) late last night, that immediately ran up against the threatened pre-moderation/editing of anything and everthing I now submit there. (The site manager says his regulars are distressed at the way I refer to some Shroud so-called experts, invariably self-appointed, and content to spout 10 a or 20 year old mantras based on cursory, impressionistic research, rarely if ever contributing any new facts or ideas.:

    Your comment is awaiting moderation.

    “Dr. Collins [Berry] has tried to prove superficiality possible by scorching an onion skin laid over linen. What folly. If you will but toss a bit of linen and an onion skin into a fry pan you can see why. The onion skin turns brown quickly. I suspect that it caramelizes at lower temperatures and much faster than linen scorches. You just don’t mess with different materials without testing or researching, not if you are a good scientist.”

    Well, there is a simple experiment I can do, or rather refine, to address that criticism. I shall simply press the hot template down with part in contact with onion epidermis, and part in contact with linen. When I have a faint or even strong imprint on the linen, i shall then peel back the onion epidermis to see if it has protected the underlying linen. I believe it should be possible to produce that result, based on some existing results of mine, unpublished, where there is very faint, incipient scorching of linen, but heavy scorching of epidermis. Yes, the epidermis does scorch more readily. I have already acknowledged that, and suggested that different chemistry operates – forming Maillard sugar-protein reaction products and pyrolysed hemicellulose/cellulose respectively.
    However, i shall add that experiment onto the end of the post describing the onion skin data. I shall not be discussing science here in future in view of the pre-moderation/editing policy now in force to say nothing of general unpleasant backbiting tone of many of the comments.
    I must also ask Dan to desist from pirating pictures and text off my site describing my original research, at least until a decent time period has elapsed, say 1 week. Would it not be courteous, to say the least, to write a brief summary and provide a link to my own site?

    Colin Berry

    I shall have a go at doing that experiment this morning, hoping that I have enough onion epidermis to get a conclusive result (involving as it does some trial and error, since I cannot see under the contact area to judge when to remove the hot metal).

    Update: the comment above, the last I shall post to that site in a proactive sense
    (defensive responses are another matter in the event of seeing one’s ideas rubbished or misrepresented) has just this minute been approved, but I do not as a matter of principle allow blogsite hosts to select bits from my comments. This site operates under a WordPress default system that requires my approval of the first comment. Subsequent ones go through without requiring approval. If a commenter were to become defamatory and ignored warnings I would simply place a block on all their comments. Yup, it’s all or nothing where this site is concerned.

    There is a lot of ignorance or misundersatnding on the other site regarding the superficial and chemical nature of the scorching phenomenon, with the word “impossible” being tossed around with gay abandon. I shall be using this thread over the next few days to pinpoint some of the misunderstanding and, most importantly, misinformation.

    It is my firm belief that a deliberate and systematic attempt is being made to expunge “scorching” from the Shroud literature. One can see this attempt going back years, if not decades, to suppress or deny what I would see as a self-evident explanation for the Shroud image. Now why would anyone want to dismiss scorching – by heat that is – as an explanation, while being eager to play around with high energy radiation (ultraviolet, x-rays, gamma rays etc)? Why go to the trouble of producing tiny discoloured blemishes on linen that might also be described as (radiation) scorches while dogmatically excluding thermal scorches, especially those produced by physical contact/heat conduction? The expression “agenda-driven research” springs to mind. And the Shroudie roadshows are clearly intended to keep alive the “mystery of the Shroud”, the “haunting” (and scarcely visible) image of which “defies modern understanding”. Complete baloney… What a circus!

  5. colinsberry says:

    From the other site (see sidebar):

    “LOL: Whoa! Why are we using onionskin? Its ranges from about 200 to 400 microns in thickness. That’s microns. That’s 200,000 to 400,000 nanometers. Onion skin is like about 1000 x thicker than the image on the shroud.”

    First, why the picture of an intact onion with some brown outer skin lying next to it – as if the latter were the onion epidermis used in my experiments. Onion epidermis is stripped off the inner white scale leafs as a thin membrane..

    Yes, the onion epidermis is a fraction of a mm thick – say 1/5, so orders of magnitude greater than the primary cell wall. So what? Have I ever said different? There seems to me an attempt to conflate two entirely different issues. One is the thickness of the image layer on the Shroud, which we are told is 200nm, which is the approximate thickness of the primary cell wall (PCW) of the flax fibril, of which there may be up to 200 per thread.

    But there is also the SEPARATE issue to do with scorching. Time and again I have been told that it would be impossible to scorch a superficial 200nm image on linen without producing a scorch that penetrates beneath the PCW or into deeper fibres. Why? All one has to assume is that the outermost cells of flax fibres accept the image onto their PCW, but the entire cell many times thicker, protects the underlying cells and fibres from scorching in the manner shown here for onion epidermis.

    The PCW of flax cells has loosely packed hemicellulose and cellulose which other things being equal are more susceptible to pyrolysis through physical contact with hot metal.than the more densely packed arrays of cellulose and hemicellulose in the secondary cell wall that underlies the PCW.

  6. Pingback: Daniel R. Porter’s ‘Troll Central’ by any other name. | The Shroud of Turin: medieval scorch? The blog that separates the science from the pseudo-science…

  7. Pingback: Scorching Onion Skins | Shroud of Turin Blog

  8. colinsberry says:

    Update: Sunday 9th March 2014

    I had reason recently to mention the reception this posting received on the Troll Central site some two years ago in what I now describe as an instance of a hit-and-run attack by one “Leland of Boston. His emailed “comments”, read trolling, were elevated by the site’s host to guest slot. Since this post is now the topic of a new posting over there, I have put together this speedy response to a selection of the more critical comments that are appearing. Some of the latter carry a whiff of vindictive troll-like character to them, attempting to destroy the credibility of this retired scientist, or to suggest that he lacks a grasp of the literature, especially re Rogers’ largely speculative “impurity coating” hypothesis, seemingly ignorant of the primary cell wall and much else besides (reactive hemicelluloses etc).
    Here’s a cut-and-paste, with their comments in bold, my replies in italics,

    Scorching Onion Skins
    March 9, 2014 Dan

    I want to call your attention to an interesting discussion going on over at Colin Berry’s site in his posting (link provided)

    First, Thibault wrote:


    “Can you explain step by step your onion experiment ? I am not sure to understand well, but I see no connection with the scorch hypothesis on the Shroud.”

    Colin Responded:
    I’m a little surprised I have to explain (all over again) what to me seems self-evident. Never mind. Let’s start again.
    And it goes from there. For more on the subject see, Modelling the image of the Turin Shroud – an interrupted experiment using onion epidermis – just one cell thick, a posting on Colin’s blog from two years ago.

    March 9, 2014 at 7:22 am | #1
    If you consider oignon is mainly made of starch and sugars, it looks like the suggested hoax recipe based on a thin external layer :
    Rogers :
    “Using a cloth washed in a low-surface-tension solution containing pentose sugars (e.g., a Saponaria solution) and dried in the sun, a non-metallic statue at a temperature above 100C might have worked.”
    A thin oignon layer doesn’t absord much heat, it protects only very slightly and briefly the linen. It is just more sensitive to lower temperature.

    Someone whose default position is the Rogers’ starch/sugar impurity layer. Where’s the analytical evidence (authoritative, that is, not semi-anecdotal) for there being an even coating of those two substances on the Shroud, or of them being in non-image layers etc etc?

    Oh, and there’s no starch in an onion. Sugars – glucose, fructose, sucrose certainly- but not starch. How difficult is it to spend a few minutes on a search engine instead of cluttering up the internet with easily-spotted falsehoods?

    As regards the thermal protection, read what I wrote. The epidermis gives excellent protection from the hot metal, when the latter still contains demonstrably sufficient heat to scorch linen. So the point about the epidermis being more sensitive to scorching, while true, is largely irrelevant. You may disagree with my interpretation, but please desist from misrepresenting the experimental observations, and/or omit to mention my crucial reference to the control experiment.

    Mike M
    March 9, 2014 at 8:23 am | #2
    I don’t get it? We have linen, why experiment on onions. Or is it claimed that the whole shroud was covered in onion? This is what happens when you perform experiments in the kitchen.

    Well, if you think some more about imaging onto linen, with at least three annular zones (PCW, SCW and cell membrane/cytoplasm) then the term “linen” becomes problematical. Which layer or layers of linen are scorched in the present Shroud, and which others may have been present initially, but have since detached through being more extensively scorches and rendered brittle?
    Yes, I like simple explanations too, but one has to distinguish between simple and simplistic.

    March 9, 2014 at 8:58 am | #3

    I guess a 4.4×1.1m linen cloth can be produced today not manually woven but I don’t think the weaving whether manual or automatic makes a difference in the image. What’s your point?
    The point is modern linen can’t be directly compared to the shroud.

    Even “manual” weaving is semi-automated, inasmuch as there will be heddles that have to be raised and lowered, so one has to be specific if one’s to make any useful comment. (What was your point btw?).
    There is some, possibly quite a lot of comparison that can be made between modern and centuries opld linen, assuming they are both retted flax fibres. Technological aids to assist spinning and weaving will differ of course, but let’s not repeat Rogers mistake of looking to Pliny for clues (saponins etc), thereby betraying a lack of scientific objectivity (his task being to prove/disprove authenticity, not to take a 1st century provenance as his working hypothesis).

    Mike M
    March 9, 2014 at 9:34 am | #4

    Sorry Anoxie, I still can’t get it. what your saying would make sense if Colin is talking about scorching an impurity layer (like Rogers postulated) but he is talking about primary cell wall. What is the difference between primary cell wall of antient linen and modern linen?

    At last. A valid point. Yes, my focus is very much on the primary cell wall (PCW) for which Rogers had a blind spot (or an inadequate grasp of botany).

    March 9, 2014 at 9:42 am | #5

    I’ve just pointed the similarities, meaning he’s got a degraded idea of what Rogers suggested years ago.

    I have done very extensive and detailed critiques of Rogers “suggestions”, and that’s the trouble. Most of ideas re the impurity layer, and the Maillard hypothesis are little more than suggestions that have not been backed up by experimental evidence. His critique of scorching was not terribly impressive either.

    March 9, 2014 at 8:55 am | #6
    But I don’t understand any heat hypothesis when Barrie Schwortz has stated over and over again that the Image doesn’t fluoresce that means it wasn’t heat induced.

    Barrie Schwortz is a photographer, not a chemist. Were he a chemist he would know that the presence or absence of fluorescence in model v ancient scorches can tell you nothing for certain unless you know something about the physical and chemical nature of the fluorescent species. Are they really furfurals as some have suggested, which are (a) volatile and (b) prone to oxidation, with loss of fluorescence over time. I suspect the fluorescent species are many and probably more complex than relatively simple furfurals. (Am not even certain the latter are strongly fluorescent)

    Mike M
    March 9, 2014 at 9:39 am | #7
    Clublu22014; I totally agree, not only that but scorched linen show up in transmitted light photography while the shroud image doesn’t. And the lumen of the fibres are discoloured while the shroud image doesn’t show any lumen discolouration. This is a prime example of how the anti authenticity camp would go to any length (not supported by science) to discredit the shroud. With the hacking hypothesis we have been seeing both extremes of the spectrum.

    Transmitted light? How can one be certain that the original Shroud centuries ago had the same properties as the one we see now, after yellowing, ageing, oxidation etc etc?
    Lumen not discoloured? The lumen is a hole, so any discoloration is likely to be due to the remnants of the original living flax cell (membrane, cytoplasm etc). Who’s to say that some fibres did not originally have extensive scorching that penetrated to the lumen interface, but compromised the core of the fibre so much as to make them break off over the centuries, leaving less extensively scorched fibres – thus creating the so-called “halftone effect” (an over-optimistic, dare one say hifalutin term if ever there was)?

    clublu22014 commented on Scorching Onion Skins.

    in response to Mike M:

    Clublu22014; I totally agree, not only that but scorched linen show up in transmitted light photography while the shroud image doesn’t. And the lumen of the fibres are discoloured while the shroud image doesn’t show any lumen discolouration. This is a prime example of how the anti authenticity camp would go to any length (not […]

    Mike this is a most excellent insight! Thank You!

    (However I am having a bit of a quandary as to just exactly what the identification of the lumen is regarding the fibril of the linen… It seems obvious that it is the outside molecules of the fibril’s tubing not necessarily the inside. Perhaps you could clarify this for me?)

    Correct, Club. See my last comment.

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