I hadn’t intended to blitz this site with comments, but the stimulants to comment keep coming, so here we go, with a very brief idea (shame that Ray Rogers is not around to respond).
If you look at the first of the graphics labelled “variegated patterns,” you can certainly see horizontal banding very clearly, but it is seen mainly where it crosses the image zones, and is scarcely visible outside those zones.
Now Rogers talks about bleaching and impurities, and how impurities reinforce the image intensity, but is not very clear, at least in the quoted passage as regards precise mechanisms. Where the latter is concerned it gets somewhat confused, because there are so many impurities listed by Rogers – lignin, which can be bleached or unbleached, conjectural starch (“impurity coating”), saponins etc. What makes his exposition ever more opaque, at least to those of us trained in chemistry and botany, is his inclusion of “hemicelluloses” in impurities.Hemicelluloses, with a significant content of pentosans, 5 carbon sugars, are intrinsic to plant cell walls, and are a major component of the primary cell wall (PCW).
There is in fact a much simpler explanation for banding than the one proposed by Rogers. It is based on that PCW, a discrete botanical entity that Rogers scarcely mentioned, if at all. The PCW is highly superficial – in other words it is the first layer of cells that one encounters when approaching a flax or linen fibre from outside. That’s because it is the first formed layer of cells in flax and other plants, and remains on the outside when the secondary cell wall is later added.
All we have to do is to suppose that it is the highly superficial and chemically reactive hemicelluloses of the PCW that were the prime target for image imprinting on the Shroud, producing yellow or tan dehydrated carbohydrates and their condensation products. Secondly, the more adherent the PCW, i.e. through having resisted flaking off in spinning and weaving, then the more intense the image. So any process, whether mechanical or chemical (as in bleaching) that strips off or reacts with hemicelluloses will lead to a lighter coloured thread, a light band in the final weave, and less intense image. Conversely, any threads in which the PCW is more intact and chemically unbleached will tend to produce a darker band, especially in the image zones where that surviving PCW and its hemicelluloses have acquired colour by whatever process caused the image.
Raymond Rogers was a gifted chemist, but sadly he seemed to have had a blind spot for the PCW.
My own botany was limited to A-Level and fresher year at University, which partly explains why I’ve been having difficulty finding estimates for the precise thickness of the typical plant PCW, but nothing I’ve seen so far would rule out PCW thinness as the reason for the Shroud image layer being a mere 200nm thick or less (as suggested) if the image is formed solely on the outside- facing PCW. Remember – the linen fibre comprises elongated single cells. (Yes they look thicker in the parent flax, but that’s because the fibres are cemented together in bundles with pectins. Retting is about degrading the pectins, with the aid of bacteria, to liberate the individual fibres that are then reassembled into threads by spinning, but are still independent fibres comprising strings of single cells).
Many moons ago I showed that one could form an intense contact scorch on the stripped epidermis from dried onion scale leaves – the latter a gossamer thin flake also just one cell thick, presumably with a PCW that is 200nm thick or thereabouts. Don’t be deceived by superficiality. Highly superficial layers can make excellent surfaces for image capture and colour production.
Who needs to invoke starch or other impurity layers when there is a receptive PCW, more in some parts than others, accounting for that banding and those differences in image intensity.
Here endeth this morning’s lesson. You can all wake up now.
Second comment (in response to David Goulet):
October 20, 2013 at 2:08 am | #5
I have noted your additions and corrections, David, but have to say that this focus on bleaching variation as a cause of yarn variation, and yarn variation as a cause of banding, and banding as a cause of bilaterally symmetrical image cut off, and bilaterally symmetrical image cut off as a cause of an overly-gaunt face strikes me not as objective science, but more as special pleading. That hunch is reinforced when one sees the entire argument being used to dismiss a medieval provenance for the Shroud.
Some might think that speculation as to the reasons for the gaunt face is futile unless one knows the mechanism of image imprinting. A point worth noting is that gauntness, in the sense of being narrower than one might expect, is a characteristic that is not restricted to the face. One sees it in the forearms too, one of which looks particularly stick-like, and in the fingers, giving rise to their description of “bony” with some even suggesting an X-ray type of imaging.
Personally I think there is a very obvious explanation for all the gauntness effects, and it has little if anything to do with bleaching or banding, and everything to do with the mechanism of imprinting. But the posting is not about that, so I’ll stop here.