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:
Afterthought: here’s the same photograph as above, with an aid to spotting the two critical regions (blue and red dashed lines)
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 http://www.tvrit.it/enea/20120103-RAI_3-COSE_DELLALTRO_GEO_1555-175825001a.ASF 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: