Forget those miraculous flashes of ultraviolet light - was the Turin Shroud produced simply with medieval technology - heat conduction and scorching?

Could the Turin Shroud have been made in medieval times as a hoax or fake, simply by scorching an image onto linen, say from a 3D representation of the crucified Christ? 

Could the latter have been a ‘bas relief’, i.e. a raised image on a background, comparable to a medallion say (albeit much larger) or even an intact statue, fully in the round, so to speak?  Was the bas relief or statue heated and then draped with cloth to produce a scorch mark corresponding with the relief (thermal imprinting).  These were questions that John P Jackson of the STURP team addressed back in the 1980s.   

 John P Jackson

Here from Stephen Jones’s splendid site is an account of Jackson’s work, shorn of references to keep it uncluttered, which I have interrupted and annotated to insert my own sceptical views (in blue).

John P. Jackson:
"Heated Bas-Relief/Scorch Theory Another possible image-forming mechanism similar to that proposed by Nickell involves pressing a stretched cloth over a heated bas-relief. Such an idea was first proposed in 1961 and tested, with limited success, by placing a white handkerchief on top of a heated small medallion that bore a carving of a horse. This theory is more intriguing than most because the Shroud image does appear to have many of the physical and chemical properties of a light scorch.  STURP scientists Jackson, Jumper, and Ercoline tried to duplicate the image on the Shroud by testing the scorch hypothesis more fully. To accomplish this, they heated a full-size bas-relief model of a face and stretched over it a linen cloth of a thickness similar to the Shroud.  The ... resulting image lacks the high resolution and sharp focus found on the Shroud.

 Later, John Jackson (kneeling) used real human models, at least those with a passing resemblance to YKW...

High resolution? Sharp focus?  I doubt whether those viewing the Shroud up to the end of the 19^th century would have described the image in those terms, indeed modern day viewers too. It was not until  the first photographs were produced that the friendlier “positive” image became available. 

The very first negative-to-positive transformation of the Shroud image (1898)

The subsequent 110 years or so have seen progressive advancements in imaging technology, bringing ever greater resolution, clarity, (claimed) realism etc. But how much is electronic and digital tweaking to produce the best picture, regardless of the information content of the faint sepia image with which scores of generations had to be content.

“While the bas-relief method seemingly yields a respectable three-dimensional image, problems are evident in the accompanying VP-8 relief of this image.

 VP-8 image-analyser

Hollow spots below the eyes, next to the bridge of the nose, below the lips, in the beard, and on the forehead are all noticeable ... . Further, a slight plateau is visible on the high spots of the VP-8 relief, similar to those produced in VP-8 analysis of results from experiments with direct-contact methods.

A respectable three-dimensional image?  I raise my hat to Jackson – those are words you will rarely see in the current Shroud literature that holds the image is genuine 1^st century AD, indeed the actual burial shroud of Christ.. Most are dismissive, indeed comtemptuous of any modelling with bas-relief etc, claiming that those techniques fail to produce ALL the characteristics of the Shroud image. And what tops the list time and time again? Yes -  you guessed it – those  claimed “3D-encoded characteristics” 

 3D image of Turin Shroud from VP-8 image analyser

Yet here we see Jackson conceding that an inanimate bas-relief produced a 3D image on cloth by simple heat conduction (”scorching”).

So the image of that bas-relief was deficient in some respects (hollow spots below the eyes etc)  Yet for centuries,  sorry to repeat myself, the eyes on the Shroud were little more than white hollows, but now, with the technology at our disposal,  it is the photographic positive (naturally) is now being held up as the gold standard!  “A slight plateau on the high spots” ? Did Jackson not consider modifying the bas-relief template, which was maybe too flat, or ringing the changes any other the other numerous variables that might have been tweaked to get a better image?  Science is about establishing principles, not replicating every tiny detail of the arts and crafts, especially as the materials used were unknown. Science needs cues if it is to make a contribution. Science cannot be expected to travel back in time to discover precisely what materials and techniques were being employed. Science  is a method, an approach, not a magic wand. Science has its limitations...

"Even though the heated bas-relief produced better three-dimensional information than other methods, Jackson and colleagues concluded that this process could not encode many of the necessary Shroud image characteristics. For example, regardless of the temperature of the bas-relief, thermal discoloration appeared on the back side of the test cloth within several seconds after being placed on the hot bas-relief. Thus, the superficiality characteristic is violated because the image could not be encoded only on the topmost fibrils of the linen."

A thermal discoloration on the back of the cloth? Would that by any chance be the “faint reverse side image” that we are told is one of the unique characteristics of the Shroud that no one has replicated, or can ever hope to replicate?

But the main characteristics we are told is the highly superficial image on the front side, so superficial as to defy modern science. Yet Raymond N Rogers provided a simple explanation for the superficiality, based on his crucial observation that the image could be stripped off with adhesive tape. The image is not on the cellulose fibrils of the actual cloth he said, or,  if it is, only on the most exposed ones. The image is formed on a layer of adhering carbohydrate that is not cellulose, but something chemically more reactive, more prone to dehydration and scorching. The latter is a matter of  speculation  –  it could be starch, simple carbohydrates, saponin  etc, all of which have been proposed, either acquired adventitiously, e.g.in linen weaving and manufacture, or purposely as a known thermo-sensitive substance that would brown on exposure to heat (think invisible ink, think gravy browning etc.). Either way, there is a COMPLETE explanation for a faint image forming on both surfaces, but not the intermediate (bulk) cellulose fibres. Cellulose, as we know, is highly resistant to degradation by heat, oxygen etc on account of its highly ordered crystalline nature -  a function of the multiple hydrogen bonding interactions between beta-linked glucose molecules. 

Here is a scorch image I produced on cotton using simply powdered charcoal as a thermo-sensitizer and heat from a 60W lamp ( photographed after washing out the charcoal). Think how much easier it would be to scorch a surface layer of more reactive carbohydrates (fruit sugars such as glucose, sucrose etc)

Other carbohydrates, e.g. starch with its alpha-linked chains in amylose and amylopectin are less stable, and simple mono and disaccharides more so, especially the reducing sugars like glucose. Simple sucrose, which easily splits to glucose and fructose, can be the agents for easy caramelisation (browning) when exposed to heat.

“The researchers tried to circumvent this problem by wetting the cloth, thereby extending the scorch time. When this technique was tried, new problems appeared. The image's contrast was reduced, causing more severe distortions in the three-dimensional analysis and resembling images obtained from direct-contact techniques ... In addition, because the cloth was essentially flat when the image was encoded, tests of this image-forming method failed to generate an image that contains the subtle lateral distortions that are consistent with the cloth-drape effects found on the Shroud."

Again,  these difficulties are less to do with science, and more to do with technology, indeed arts and crafts, difficulties that can or could have been be overcome by trial and error. Mimicking “subtle lateral distortions” may require nothing more than a stretching and/or ironing technique, instead of simply draping cloth over a hot template.  

These are the Italian scientists who think you need high energy ultraviolet light to scorch an image onto linen (at a distance, focusing system  unspecified). 

  and this is their equipment for modelling a 1st century miracle (leaving a superficial scorch mark on cellulose)

Returning to Planet Earth: what about Jackson's Hot Statue method?  Critique to follow...

Effect of twiddling the gain control

This I believe to be the way to go (but replace the person with a bas relief template or statue): and spend time on ringing the changes with those critical experimental variables, too numerous to mention:

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