Friday, December 30, 2011

The Turin Shroud - could it have been produced by thermo-stencilling?

Photographic negative with enhancement: Image now a "positive".

This is a quickie post. I'll tidy it up later. It's to show some comments I have today posted to Tom Chivers blog on the Daily Telegraph with the germ of an idea (that may or may not be original).

Tom's topic title: 

The Shroud of Turin: forgery or divine? A scientist writes

The comments set out briefly an idea that came to me suddenly this afternoon as to how that image on the Turin Shroud may/might have been produced in the 14th century by medieval "forgers", intent on producing yet another 'holy relic' to add to fragments of the 'real cross'  etc etc. Yes, holy relics were a major growth industry in the 14th century, given they could attract thousands of pilgrims to your cathedral or whatever each year - the beginnings of the travel industry...

Comment 1:

'THERMO-STENCILLING'? (don't bother googling - you read it here first ;-)

The crucial detail is that the image is a negative, i.e. parts of the original object that were well illuminated ("light") look dark and vice versa.

A negative image might at first sight suggest some kind of photography, either early primitive, or entirely accidental, or a combination of the two.

Leaving aside the nature of the photographic emulsion and photosensitive compound there is a problem with production of any image by photography. It needs either a good convex (converging) lens to bring light rays to a focus, or failing that a pinhole camera. It seems improbable(though not impossible) that either of those technologies were available even 800 years ago at a sufficient state of development, since if there had been there would surely be a host of other artefacts available from that era (e.g. grainy photographs of royalty?).

But there is another means by which an image can be produced that does not need photography, or at any rate the focusing of light from an object. One could use 'thermo-stencilling" instead. How? By taking some white fabric, and fashioning an image using black charcoal as one would a portrait, using degrees of shading rather than a line image. One would then expose the cloth to radiant heat, say from a furnace. The black areas would absorb heat and partially scorch the cloth in immediate contact with the charcoal while the white areas would reflect light and remain unscorched. The final step would then be to wash the particles of charcoal completely out of the cloth, leaving just the brown image - and  if I am not mistaken it would be a negative image, assuming the artist used the charcoal lightly for light-reflecting features of  a man's body, and more heavily for the bas-relief features that are in partial shade or reflect less light     Oops - sorry about that. Thanks Mouse (comments)  for pointing out that silly error.

By washing out the charcoal, the observer sees no evidence of the the image having been "painted" on the cloth. All that is left is a scorch mark - and being formed under a charcoal coating, it may be subtly different perhaps from one formed by direct action of hot iron or heat rays onto fabric.

Comment 2 (omitted, largely clarification in response to a query from xxxxxxx)

Comment 3 - further clarification:

Sorry, xxxxxxx  , but I don't understand your difficulty re charcoal. If you had been barbecuing, and had got charcoal dust on your shirt, would you throw your shirt away, on the assumption that it was impossible to wash out? Surely not. Even without modern detergents, charcoal, which is simply microcrystalline graphite, i.e. sheets of carbon atoms arranged as fused hexagons, giant molecules in fact, should be relatively easy to wash out.

You are not by any chance confusing charcoal with scorched or charred cloth by any chance? The procedure I propose starts by drawing on a cloth with the kind of charcoal given out in school art classes - carbonised twigs. The cloth is then "grilled", i.e. exposed to radiant heat, e.g. from red hot coals, or again, charcoal, though I hesitate to mention it, and the black, charcoal-coated areas on the cloth will heat up - and become scorched - in contrast to the white reflective areas without charcoal that will remain relatively unscorched, at least with short exposure times.

I only suggested charcoal because it is "right for the period" and probably does the job, but other black substances might serve equally well, given that black subsrtances absorb heat as well as light, provided they can be washed out after heating so as to "dispose of the evidence" so to speak as to how the negative image was produced. Please tell me if I am not making sense.

Again, I thank you for your interest, but have to say I am somewhat disappointed by the response so far. Any feasible mechanism should surely place a big question mark over the assertion of those Italian scientists that there is no known mechanism by which the image could have been produced. I maintain there is - and I have chosen to call it "thermo-stencilling".


Tomorrow I must get hold of some charcoal, and see whether or not  the idea works as predicted. I'll use a hot ring on the cooker hob as a source of radiant heat.

Update: Saturday 31 Dec 2011    I've just this minute cut up some cotton pillowcase (OK, so it's not flax/linen as per original Turin Shroud) and then cut some batten as per piccy below to create grips - left and right - that allow the cloth to be held close to a source of radiant heat without barbecuing knuckles.  Missus will add artist's charcoal to her shopping list when she goes into town this afternoon.

While waiting for the charcoal. I have been giving thought to what to use as a source of radiant heat.  The initial idea was to use the cooker hob:

But there's a potential complication there - it's not just radiant heat, but hot rising convection currents as well. It's better to isolate and study one variable at a time.

The new ceiling spots in my bathroom throw off a lot of radiant heat - downwards - in the opposite direction from rising convection currents, so I will try holding my "miniature shroud" up close to a spot.

Update  Sunday 1st Jan 2012

Well, missus was unable to get hold of artists' charcoal stick, but never mind, we'll try barbecue lump charcoal:

Watch this space folks (will try "grilling" under a spotlight as soon as missus has vacated the bathroom).

OK, so here's the charcoal outline being exposed to radiant heat from a ceiling spot, with the charcoal-side facing the lamp. Within a few minutes I began to see a sepia smile appearing on my side.

And here is the reverse side back on the table after just a few minutes of gentle grilling.  Prediction confirmed!  'Thermo-stencilling' WORKS - and given the utter simplicity of the procedure may or might well have been the method used 800 years ago to produce the Turin Shroud.

The final step is to wash out the charcoal, leaving hopefully just the scorch mark (with no clue as to how it was formed!)

Here it is after a brief rub with soap and a rinse. Not all the charcoal is removed, but enough to see that the image is now mainly in the form of a scorch mark.

The final step is to dry over the heated towel rail:

Incidentally, if you are wondering why the whole face (and those ears) are not brown, it's because of the limited diameter of my ceiling spots. I used one (60W) in the living room - bigger than the bathroom I had originally intended to use but the diameter is still only 7cm approx.

What might have been used as a souce of heat 800 years ago? Maybe a kiln or furnace (lime? glass?) with the door open...

Have just this minute posted this to Tom Chivers blog:

"Hello again everyone (and a Happy New Year to Tom). Guess what? I have just reproduced a downmarket version of the "Turin Shroud" in miniature, using simply a cotton sheet, a lump of barbecue charcoal, a source of radiant heat and a bar of soap. It's all on my own science buzz blog:

newsjunkie aka sciencebod

PS: Methinks, or rather mesuspects, that none of this will come as a surprise to the canny, well-informed Vatican ...    ;-)"


Anonymous said...

Interesting. Didn't the Dutch Masters use the camera obscura to get perfect 3D perspective? An image copied carefully using charcoal and a camera obscura would obviously contain all the 3D 'coded information' which seems to be baffling the scientists. You could be onto something here...

sciencebod said...

Well, you have raised the 3D angle, which I suspect will be a major one that needs to be addressed. I don't intend to say much until I've done some more reading. For the moment, I would just express scepticism re that term "coded information". If an image is photographed and then digitized into thousands of pixels for analysis, then what would the discovery of encoding mean precisely? Hidden coding in the original image, as implied, which seems improbable, or coding as an artefact of digitization?

Is there not a sense in which the skill of the artist in making a 2D image seem at least partially 3D-like - through light and shadow to represent relief and contours - is to fool the brain's mechanisms in the visual cortex to "decode" images received as a series of nervous impulses from the retina. That might then be detected as "coding" after digitization, but merely reflect the skill of the artist in making 2D seems quasi-3D.

"Coding" and "decoding" then is arguably a can of worms unless a clear distinction is made between what the brain is doing, as distinct from the computer of an image-analysis expert using his sophisticated but possible too-clever-by-half statistical and modelling techniques.

I hope some of that makes sense. Thanks for the interest.

MouseInTheHouse said...

wait a minute that is not a negative and it can;t produce3D data, no it can;t. it can;t be doubly superficial or pixelated like the shroud.i;ll bet thermal stencil images fluoresce under UV light. try it. shroud images do not. major fail.

sciencebod said...

Thanks Mouse. I just tried responding to your same comments over on Dan's site, but WordPress does not seem to accept my login and the commenst has not appeared.

Here it is:

"MouseInThe? is absolutely correct when he says that a thermal stencil image is a positive, not a negative, since dark charcoal-covered areas become dark scorched areas. I thank him for the opportunity to back-track a little on what I may have said previously, or at any rate to qualify it.

To produce a Turin-Shroud like negative, one that becomes a positive on the photographic negative, then the hypothetical sketched image would have had to be drawn as a negative, with a reversal of light and shade, which is admittedly unconventional.

But there may be strong practical reasons for doing so given the proposed technique: in a well-illuminated subject there will be a predominance of light reflective areas over ones that are in shade (eye sockets and the like). That would tend to give a scorch pattern with just a little scorch, but an awful lot of white space. By reversing lighjt and dark in the sketch, one ends up with something that makes a much bolder image but one that is still recognizable as a man, despite the reversal of light and shade.

I hope that makes sense..."

Could you oblige by cutting and pasting into Dan's blog. I'll try and sort out the WordPress thing later. Odd, because I am able to post comments to another WordPress blog without being pre-registered for that site...

sciencebod said...

PS: the site in question is Dan Porter's splendid "Shroud of Turin Blog" which has very generously devoted a post to my little experiment with the lamp and charcoal:

Here's the link:

sciencebod said...

Have posted this comment to "Shroud of Turin" site re the claim there that heating could not have produced the image, based on what I would regard as somewhat tendentious reasoning and/or assumptions, eg. that heating would disturb the structure of otherwise unaffected cellulose:

"I overlooked to thank MouseintheHouse earlier for agreeing to transplant a comment from my own blog prior to my (re)registering with WordPress, to say nothing of Dan Porter for responding to an email almost instantly with this post. Many thanks to you both.

It seems somewhat uncharitable then, to say the least, to immediately take issue on the details, but hey ho, that’s science for you.

While my knowledge on many of the issues is patchy, there is one apparent discrepancy that strikes the newbie quite quickly. On the one hand we read that the image is exceedingly superficial, scarcely penetrating into the fibres, yet above we read that if scorching were the mechanism then we would expect to see changes in the structure of the flax fibres. I do not see the latter as in any way self-evident, far less obligatory, if one supposes that scorching affects the most superficial top surface only. Indeed, if a sketched image in charcoal or a similar black pigment were used to absorb radiant heat, as I have suggested, that might also tend to restrict scorching to a very small depth of penetration, such that fibrils look relatively intact immediately below the scorched layer… In other words, the carbon particles serve to protect deeper layers.

There is also a recent paper on cellulose pyrolysis that starts by listing the initial depolymerisation products – levoglucosan, furfurals etc – and then makes the interesting observation that char is formed by re-polymerisation of the decomposition products (rather than stripping out of volatiles, say, to leave a C-skeleton).

Given that the monomers for the secondary polymerisation are small molecules and volatile, at elevated temperatures they will tend to diffuse rapidly from their sites of formation into the surrounding air. So there are further grounds, albeit theoretical ones, for thinking that the scorched zone could be very superficial indeed, resulting in minimal damage to fibrils at a gross level observed by light microsocopy or possibly even SEM."

sciencebod said...

Afterthought: how superficial is my homemade scorched image? Is there anyway that could be approximately gauged without using specialized equipment?
One could try abrading the surface lightly, say with fine-grade sandpaper, one stroke at a time, to see if the image can be removed without "roughing-up" the fabric too severely. Another idea has just occurred to me - to see whether the image can be stripped off with sellotape. That was the trick used to strip individual sheets of graphene off graphite - winning the discoverers a Nobel prize no less! Separation of the lamellae of graphite requires breaking the adhesive van der Waals forces between the carbon sheets, produced by temporary electrical dipoles which though much weaker needless to say than full covalent bonds, can be sizeable when there's a lot of them holding the two slices together. I'll give it a try later in the day, and may also experiment with applying charcoal as a water-suspended paste, i.e. painting it on the cotton with minimum applied force. Much depends on whether the char particles are bonded in any way to the cellulose matrix, or are free-standing, so to speak...

Incidentally, my reading of the pyrolysis paper cited above would suggest that cellulose char ie scorch mark, is not elemental carbon ("charcoal") but polymeric material with hydrogen and oxygen as well as carbon. It might be better described as a resin rather than a "char". Clearly there is a lot more reading that needs to be done to get a better understanding of the surface scorching of cellulosic fabrics...

sciencebod said...


Since this post was written, this blogger/retired science bod has proposed a more comprehensive theory as to how the Shroud was created in the 14th century as a ‘holy relic’. The essence of the theory is the making of a thermo-stencil, using linen impregnated with a heat-sensitive chemical substance or cocktail, from a partially-mummified, minimally-skeletonised cadaver possibly in a monastery (think Brno). The desiccated proxy for the crucified Christ would have been heated in an oven of some kind, until radiating sufficient infrared as to be capable of leaving an image on thermo-sensitized cloth.

link to mummy theory