(This is a follow-on from my immediately preceding post)
It’s one thing to invoke an impurity layer to account for image superficiality – or, alternatively – my preferred explanation – the primary cell wall (pcw). (See two of today’s comments* on the shroudstory.com site)
A layer of dehydrated/oxidized/pyrolysed polysaccharides and/or lignin does not need to be thick to be easily detected by its yellow or brown coloration, even if that layer were a mere 20o nanometres thick (1/50,000th of a millimetre). That, after all, is the thickness of gold leaf as used for gilding and/or illuminating manuscripts – which in expert hands can produce an end-result that is virtually indistinguishable from the reflective face of a solid gold ingot viewed face-on.
However, it’s a supposition too far to invoke that same surface layer in attempting to account for fibre fracture. For a fibre to break, the entire width/diameter of the fibre needs to break.
While the structure of that fibre at the nodes/dislocations – described as “weak points” – may not be known in detail, it seems reasonably certain that there must be at least some continuity in the cellulose fibres through those nodes if the fibre is to be
reasonably sufficiently strong to fulfill its botanical role – i.e. offering stiffness and support.
However, I have seen references to there being a reversal of the helical configuration of the cellulose fibrils at the nodes.
“The cross markings, known as nodes, on flax fibres give them their characteristics microscopic appearance. There may be up to 800 nodes in a single flax fibre cell. Nodes are fissures in the cell walls and indicate a change in the spiral direction of the fibrils which constitute cell walls. Spiralling imparts strength to the cell and hence, to the flax fibre. The polygonal cross section of the flax fibre cell is typical of most plant cells.”
e.g. Ritu Pandey (2009) http://agropedia.iitk.ac.in/content/etymology-flax
So while there may be continuity of cellulose at the nodes, there may be weak points due to an interruption in the packing and crystallinity of the cellulose – making it especially vulnerable to thermal or other energy – relative to the bulk cellulose in the internodal regions. One could speculate that the internodal regions have a supporting grommet-like collar of hemicelluloses and woody lignin which stiffen joints that might otherwise flex excessively when subjected to mechanical shear forces, as exist when flax plants are battered by wind. One could speculate further that the image-imprinting mechanism degrades that nodal cement in the same way that it degrades the surface layer of the fibres elsewhere, and in so doing exposes semi- or non-crystalline cellulose that is then degraded as well, causing spot breaks in the cellulose chains and fibrils, causing the entire fibre to fracture across its entire width.
It will be interesting to see whether nodal fracture can be produced in model systems subjected to thermal or other insults, and then to see whether similar breaks can be detected in the image-bearing regions of the Shroud, ones that are absent, or largely so, in non-image-bearing regions. The latter, if found, could serve as an important signature or indeed clue as to the mechanism and source of input energy that produced the Shroud image.
Comments from shroudstory.com
* Hugh Farey, January 1, 2013 at 7:57 am | #1
What a magnificent collection. Thank you, Yannick.
Isn’t there always a however? Fanti, Botella et al.’s paper ‘Superficiaity,’ quoting Jumper, specifically mentions: “the linen fibers seen on the body-image tapes are shorter and more fractured than those from nonimage areas.” This suggests that the material of the cloth itself, not just the ‘impurity layer’ was affected by the image forming mechanism.
anoxie January 1, 2013 at 8:27 am | #2
This is an interesting point.
The aging and mechanical properties of the flax fibers may be directly influenced by the integrity of the pcw.
The reacting/impurity layer may be thicker/deeper at dislocations.
PS: here’s another image I have found showing flax fibres with very prominent nodes. These are shorter fibres, used in papermaking (bank notes etc) but flax all the same. Link to source.
Update: comment from ‘anoxie’ on shroudstory.com