imageIs Colin Berry going to be able to show how a medieval forger did it? He thinks so. He explains in a new posting, let’s focus on that hemicellulose coating on the linen fibres:

Yup, I now believe that hemicellulose is the key to understanding the nature of the image on the Turin Shroud – and yes, the latter has most if not all the characteristics a heat-induced scorch, but a highly selective one that was largely confined to the hemicellulose coatings of the fibres, leaving the cellulose cores largely unaffected.

Why do I say that? One of the major challenges has been to explain the highly superficial nature of the Shroud image, reckoned to be a mere 200nm (that’s approximately the thickness of gold leaf) , so thin and weakly attached that it can be stripped off with adhesive tape,  as described by the late great Raymond Rogers, the so-called half-tone effect.

Let’s do a thought experiment to see how that Turin Shroud could have been produced using simple technology that was available in medieval times, supported by a theoretical framework that is in tune with physics, chemistry and botany.

and then

But there is another curious detail about the Shroud image which is capable of explanation in the hemicellulose model, and once we have addressed that we shall be in a position to explain the so-called “half tone “effect.

Whereas the pyrolysis (“heat-induced degradation”) of cellulose is endothermic, i.e. requiring constant application of heat to be sustained, the pyrolysis of hemicelluloses is reported to be exothermic ( see previous post) In other words, once started it can, in principle (thermodynamic principle that is) be continued after the initial source of priming heat has been removed or gradually conducted away). A burning match is a model: provided it is held with the lit end slightly down, it will continue to burn, because heat from the flame provides the energy for pyrolysis of fresh wood, carbonising it, releasing more flammable gases, allowing more combustion, more flame, more pyrolysis, and the potential for a runaway reactions . I believe there is a low-level (flameless) conflagration, a micro-runaway reaction if you like, when hot metal encounters hemicelluloses-coated fibres: the hemicellulose pyrolyses (“chars”) where it is in immediate contact, but a spreading zone of pyrolysis then runs around the complete encircling cylinder of hemicelluloses, leaving a bare, largely untouched core of cellulose. That would explain the thinness of the image (representing the primary cell wall/hemicellulose thickness) but would also explain the fact that the image is in the ENTIRE coating of each of the (relatively few) affected fibres.

We are now in a position to understand the half-tone effect. The latter description refers to a curious feature of the Shroud image. It might have been expected that where the image is most dense, each fibre would show a greater degree of coloration. That is not in fact the case. Image areas are a mixture of coloured and uncoloured fibres. A denser image represents a greater number of coloured fibres per unit area, but coloured fibres are all said to be much the same hue. In other words, there is an all-or-nothing effect about image-forming at the level of individual fibres. The hemicellulose model accounts for that neatly. . . .

Or will it be just another in a long string of failed attempts to duplicate the shroud? If he only does thought experiments, will he nonetheless create a legend, one that many people will buy into. Will he be remembered as the scientist who did it, almost did, could have done it?

Much more, so read the full posting on his blog: The Shroud of Turin – let’s focus on that hemicellulose coating on the linen fibres … It could explain a great deal | Spotlight on that Shroud of Turin – without all the hype