Sunday, March 8, 2015

Is the Shroud of Turin image really "enigmatic"? See this straightforward, no-nonsense modelling exercise.

There be more where this came from - read on if you dare

One often sees or hears the Shroud image being referred to as “enigmatic”

Adjective: enigmatic

"Difficult to interpret or understand; mysterious."

Indeed, there's even a "Shroudie" site (and they don't come much Shroudier!) that calls itself "Shroud Enigma".

A "Multifaceted" Enigma, no less...
Given that the TS is thought by some to depict the actual image of the crucified Jesus on his burial Shroud from 2000 years ago, it’s perhaps not surprising that some have read “enigmatic” to mean not just "mysterious" but “supernatural”.

Personally. this retired science bod is quite happy to entertain the possibility of certain phenomena being supernatural, but only if non-supernatural explanations have been carefully considered and rigorously excluded.. Thus I'm minded to think that the "Big Bang" was the work of a supernatural entity - though that has not prevented me proposing a non-supernatural explanation (see margin notes) that uses conventional physics. 

Rigorous filtering out of non-supernatural explanations is sadly not the case where the Turin Shroud is concerned -  there being little real science and a surfeit of pseudo-science aka tosh.. One has only to peruse the headlines that have appeared from scientists ("scientists"?) in recent  years.  Try googling  turin shroud to find entries like this one which as it happens was what sparked my own (renewed) interest in the Shroud, after lying dormant since the 1988/9 radiocarbon dating.

If the radiocarbon dating is correct (yes, it needs confirming with a wider range of sampling sites) then the Shroud is not 2000 years old, but more like 650 years, give or take, with a birth date round about the first recorded showing of the TS at Lirey, in the rolling plains of the Champagne region of France in 1357 approx.

 Let’s suppose it is medieval. Then how come the image is “enigmatic” if man-made, not supernatural?  What features cause it to have acquired that tag, and why has science allegedly been unable to explain its peculiarity, far less to model it in the laboratory? Or can it? Is it really “enigmatic”? Or is that self-serving hype, the kind to which TV documentary makers are so enamoured?

Those seeking a comprehensive review of all the peculiarities of the Shroud image, whether real and authenticated, or claimed and maybe not well established, are in for a bit of a surprise and maybe disappointment. You see, this posting focuses on just 4 features.  What’s more they are the headline features-  the same ones about which millions of words have already been written. I refer to:

1.  “negative” photographic character

2.  its “non-directional” character (no obvious source of angled illumination, with resulting shadow bias, no brush strokes etc).

3.   its “encoded 3D” properties,

4.   its (alleged) extreme superficiality.

These are all the so-called “macroscopic” properties. I shall say nothing for now about “microscopic” properties (see same link), or about fluorescence, or lack thereof, for reasons that I’ll discuss in another posting. Suffice it to say that this blogger is somewhat dubious about claims for microscopic fibre characteristics that are (apparently) not based on viewing teased-out individual fibres, but upon entire skeins of bunched-up fibres, as in the Mark Evans photomicrographs. Good photos, yes, but not fit for purpose re 'microscopic' image characteristics. Nuff said.

So what could this humble blogger have to say that has not already been said, in many instances more eloquently?

Well, we’re told it’s not what you do, it’s the way that you do it, or, rehashed, it’s not what you review, but the way that you review it. I’m going to review the 4  chief features of the Shroud without a single image of the Shroud itself! Why? Well, I hope the reasons will become clear.

Why adopt this approach?  Answer: it’s an attempt to keep the polemics on the back burner (and of polemics there’s plenty, indeed a surfeit in sindonology (or shroudology as I prefer to call it). Let’s re-examine the “enigmatic” nature of the TS image, especially its headline features, and do so dispassionately.  At each step of the way, let’s ask ourselves this. Are they really as enigmatic as claimed? Oops. A polemical edge is already starting to intrude, so let’s go straight now to the step-by-step processes that have been used to analyse the Shroud image, but choose a model system that is stripped of emotive imagery. Let’s take the Shroud out of shroudology..  Let’s see how a different image responds, indeed an entirely synthetic, unquestionably  “ man-made” one. Let’s ask whether the adjective “enigmatic” would ever be applied to the image transformations that you are now about to see.

Starter image: I wanted one of a rubber stamp with lettering. But not a real one, at least not initially. (See tail end  for quickie test with a real date stamp). Why start with a make-believe stamp?

1. Because I wanted the raised lettering to appear white on a dark background (real ones usyally have black or coloured rubber) so as to start with what unequivocally is a POSITIVE image. (highest relief is lightest part of the image, due to unobstructed light reflection).

2. Because I wanted the lettering to be the “right way round” initially, not reversed as on a real-life rubber stamp.

This 3D template, designed for imprinting a 2D image of itself, would first be used to create an imprint of itself. The latter would then be taken through the same sequence of steps to which the TS image has famously been taken, starting with a simulation of Secondo Pia’s positive-to-negative conversion, followed by 3D-rendering. The process would then be played backwards, looking separately at reversion from negative to positive AND reversion of left/right "mirror image" changes. 
 Put like this it may seem excessively laboured.  In fact it’s anything but, we shall see, simply  by letting the pictures tell their own story, with minimalist captions.

I shall now post the graphics, then hit the "Post" key. My own interpretation (and hopefully that of others) can wait till tomorrow or later.

Fig.1 This image is not a real rubber stamp, needless to say, but made using ImageJ to look like one. It's entirely man-made, deliberately so, to be used as a 'thought experiment' in what follows.

Fig.2. Imagine the "rubber stamp" was coated with black ink. Here's how the imprint would look. It's light/dark reversed (like a photographic negative, though not one).  It's also left-right reversed - like a 'mirror image'.  However, those two features can be easily separated, arising  as they do for different reasons

Fig.3  As I say, negative image and mirror image are not inseparable (see above). One can easily restore the initial left-right configuration with photoediting software (ImageJ used here) while retaining the negative image.

Fig.4  To press home the point that negative and mirror images are not one and the same thing, even if happening together in the same imprinting operation, here's an image in which the original positive character has been restored, again in ImageJ, while preserving the reversed (mirror) image.

Fig.5. So far I have modelled the result of employing black ink on the "rubber stamp", making it easier to produce comparisons with photographic negatives. But the Shroud image is not black but faint yellowish brown. It's as if our rubber stamp had been coated with that colour instead of black.

Fig.6 But let's not allow the discussion to get too coloured (literally!) with Shroud imagery. To stay on the scientific straight and narrow, let's recall that any coloured image can be easily converted to 'gray scale' to avoid complications, that yellow above becoming grey, rather than jet black.

Fig.7: One can always use a photoediting program to convert grey into jet black, so as to reduce still further the possibility of a coloured (yellow or other non-black) imprint behaving unpredictably in further image processing.

Fig.8 So what started as a yellow-brown rather than black imprint has now been converted to one that is virtually indistinguishable from the black imprint of Fig 2, especially as it has now had a left-right flip too. Any enigmas so far?

Fig.9: Goodness gracious! What has happened here? I've taken the yellow-brown imprint, uncorrected mirror image, and put it into ImageJ's 3D rendering program. I've pretended I knew nothing about the original 3D of Fig 1, and simply adjusted settings arbitrarily to get a huge 3D response.

Fig 10:  As I say, the settings are entirely arbitrary if one knows nothing about the original template from which the imprint was obtained. In the case of the Shroud, it  could have been fully 3D in a pro-authenticity model, or much flatter, like a bas relief, in a medieval scenario. Here the settings in ImageJ have been reduced to give an "embossed look" with minimal 3D rendering.

Longstanding quote from the sidebar  of Dan Porter's my bolding

"No one has a good idea how front and back images of a crucified man came to be on the cloth. Yes, it is possible to create images that look similar. But no one has created images that match the chemistry, peculiar superficiality and profoundly mysterious three-dimensional information content of the images on the Shroud."

Er, what's so profoundly mysterious Dan about 3D-rendering? Any 2D image can be 3D rendered, provided there's some appreciable stepped gradations or (better still) smooth gradients of image intensity. The 3D-rendering programs such as ImageJ simply convert image intensity to apparent height above a base plane to create pseudo-3D. The settings one selects are entirely arbitrary and indeed subjective if one has never seen the template from which the 2D image was derived., as is the case with the Shroud of Turin, where all we have is the imprint, comparable to Fig.2 above, with no Fig.1

Image superficiality? (Sorry, no graphics).

See this link from my posting immediately preceding this one.

Rembrandt thickened paints with flour

It quotes the typical thickness of oil paint on old Rembrandts as being approximately one-thousandth of a mm, i.e. 1 micrometre, or 1000nm. Granted, that's greater then the 'guesstimated'  thickness of the TS image. (Not measured directly, I hasten to add, simply  assumed to be of the same order as the wavelength range of visible light, being based upon inability to "see" i.e. resolve the image in cross-section under the microscope). Now then, if  highly visible artist's paint with flour thickener can be as thin as 1000nm, it's not difficult to see how an image layer at the limit of visibility could be even thinner. What if the image layer were a faint  scorch, or, better still me(currently)thinks  Joseph Accetta's DYE imprinting  (now this blogger's preferred hypothesis in place of a previous fixation with thermal imprinting aka scorching.)   That's even supposing that the image today is  still that of the chosen dye bonding to linen. As suggested here previously, it's not impossible that what we see now is merely a 'ghost' image that survives after the dye has faded.  How might that happen?  One possibility is that alum (potassium aluminium sulphate) was used as a mordant to attach the dye to the linen. But alum is strongly acidic (it hydrolyses in water to form sulphuric acid). The latter could gradually cause faint but permanent discoloration of the most superficial part of linen fibres via chemical dehydration (a process that mimics scorching by heat) and those coloured caramelised products might survive long after the dye has faded.

Already there seem no good reasons for describing a 200-600nm image thickness as "enigmatic".  "Not beyond the realms of expectation"  would seem a more fitting less hyped-up description -  hardly the stuff of enigmas.

Conclusion so far: there is really nothing in the Shroud's image - at least at the macroscopic level - to justify describing it as "enigmatic". Its properties are entirely consistent with those of an imprint obtained from a 3D or bas relief template - namely a negative (with obligatory light/dark reversal), a mirror image (left/right reversal, due to a template being turned through 180 degrees towards linen, away from operator*), non-directional character (being an imprint, not a portrait relying  on light/shade to hint at form, i.e  "3D-ness", and probably superficial, given that a dye (or less probably a scorch) was used instead of paint to simulate the faint aged imprint (sweat?) that a deceased victim of crucifixion  might have left on linen many centuries earlier.

* Whilst inconvenient, one could deploy a rubber stamp in a manner that did not requiring turning it away from one, e.g. by pressing a sheet of translucent paper DOWN onto the ink-coated stamp face-side UP,  and then viewing the result through the thin thickness of paper,  with a sheet of glass as support. In that situation, the image, while still a negative of the original, would now be the "right way round". The negative and mirror images are entirely different phenomena arising for entirely different reasons.

Afterthought: coin imprints! There one has the template (coin) face up, with paper on top, so there's no mirror image reversal:

Negative imprint, but NOT a mirror image due to imprinting geometry.

As above, after tone-reversal.Now back to a positive image, the highest relief looking more light-reflective.

Yes, they can be 3D-enhanced needless to say. But it's PSEUDO-bas relief, guided by knowledge of coins.

Taking all these points into consideration, I repeat: there appears to be nothing in the least bit enigmatic about the Shroud image. It's exactly what one would expect of a contact imprint, as can be modelled, as above, with a rubber stamp, real or imaginary, as distinct from a painting or with coin-rubbing (manually assisted to ensure best contact between relief and surface). When was a rubber stamp imprint or coin-rubbing ever described as enigmatic?

Addendum: as stated here and elsewhere, this blogger now aligns himself with Joseph Accetta in  thinking that the TS image was probably dyed onto the linen, rather than heat-scorched. (I would not have rated dyeing per se very highly, but for the fact that dyeing onto linen is difficult without use of a mordant, that the most common mordant - alum - is highly acidic, and that sulphuric acid from slow alum hydrolysis may explain the faint ghost image we see today (so I've gone beyond Dr. Accetta  somewhat). So how does printed fabric respond to the conversions outlined above?

I've chosen a printed fabric that obviously has no 3D history, but which shows some stepped changes in image density.

Here we go:

Printed cotton from image files

As above, after light/dark reversal in ImageJ (yes , I should maybe have converted to B/W, but these images are prettier).

As above, after 3D enhancement in ImageJ.
It cannot be said too often: ImageJ can be used to give pseudo-3D rendering to images that have no 3D history, simply by converting image density to pseudo relief on an imaginary vertical (z) axis.  There is no mystique where 3D enhancement is concerned (and certainly no "encoding" of 3D information can be assumed in a 2D image, merely because it responds to 3D-rendering).

Yes. I have some alum on order, and yes, I shall be attempting to model a ghost image on linen offcuts using alum and water pastes in varying proportions, or even dry powder, followed by exposure to moist atmospheres. There's still everything to play for in 'experimental Shroudology.'

Further thoughts: the chief drawback with any wet ink or dye technology was the risk of seepage through to the reverse side and, as we all know, there's no reverse image, at least not one that is visible to the naked eye (digital enhancement, as per Fanti et al, has revealed a 'second face' but it's hard to know whether that is real or artefactual).

The game changer is the possibility that a mordant was used. ("mordre" - French verb, infinitive, to bite). Yes. anyone can quickly "dye" linen or cotton, but will the intense colour  still be there in a year or two, especially after laundering? Mordants give the dye a real "bite" on the cloth such that the coloration is essentially permanent. (Whether still visible after the passage of centuries is another matter).

Might we finally have a handle on the Shroud-imprinting technology by assuming Accetta is correct with his dyeing, but taking it a stage further? Suppose alum had been used  as a mordant, applied first to impregnate the linen. Then suppose the dye imprinting was done, so that the dye attached quickly to the surface mordant, so there was no appreciable reverse-side coloration. Suppose the dye gradually faded, but the mordant slowly released sulphuric acid on exposure to moist air, and that the concentrated H2SO4 produced as a result of subsequent evaporation  then proceeded chemically to dehydrate and discolor the surface fibres of the linen, such that, centuries later, what we see is primarily those "ghost" yellow fibres.  Might it be possible to model that process (see above)?  We shall see.

Reminder: This blogger, being impressed initially by the ability of contact scorching to reproduce many of the crucial Shroud properties (but annoyingly not alleged absence of fluorescence under uv)  had found  a rationale for scorching through the linking by Noel Currer- Briggs of the de Charnys of Lirey (Geoffroi and Jeanne née Vergy) genealogically to an alleged Templar uncle (Geoffroi de Charney) and thegruesome events of 1314 (slow death by roasting over hot coals). Some curious features on the Lirey Pilgrim's badge sustained that 'symbolic scorch' model.

Everything then changed with detailed descriptions from Ian Wilson and others of the recently discovered Machy mould for a second Lirey badge, with an additional motif that I (and perhaps I alone, c'est la vie) consider to represent the Veil of Veronica. Might that be a hint that the Shroud was to be seen, not as a scorch imprint, but a sweat imprint? If so, how might a medieval artisan set about simulating a sweat imprint? It might have used light dry scorching to simulate an ancient sweat imprint, but was more likely - one would have thought - to have used some kind of wet chemical treatment, if only dyeing, while still needing a template to account for negative imprinting etc. That's where my thinking began to dovetail with that of Joseph Accetta's, except I see an additional role for a sulphuric acid  'impurity' in producing a secondary faint but more permanent ghost image, one that in passing has a resonance with Luigi Garlaschelli's ideas (sulphuric acid-contaminated artist's red ochre).

Pomegranates have been used as a source of yellow dye for millennia (there's said to be a mention in the bible!).

Here are two fascinating images I've discovered through googling. They show the effect of dyeing with pomegranate extract, either used "as is", with no further additions, OR with a mordant. The latter? Alum of course!

Pomegranate dye, without mordant (left); with mordant,right.

See this article of the 'Folk Fibers' site.

Update: have today bought a real date stamp from my local branch of Poundland for the princely sum of ...  yes, £1 (oh what a lovely recession).

This scan of the imprint, followed by B/W reversal in ImageJ, followed by 3D enhancement. says it all.There was serial stamping from top to bottom without reloading with ink. Note the way that the 3D response falls off with image intensity.

Update: 13th March

The alum has arrived, express delivery (parcel postage 3 times the cost of the chemical!). Have  seen its mordanting action with my own eyes, tested using a home-made dye extract from pomegranate rind.

Have hit on a simple way (in principle, assuming no unforseen hitches) in discriminating between the dye and any H2SO4-induced "scorch" forming underneath the dye/mordant combination. One adds diluted sodium hypochlorite after treatment /storage that selectively bleaches the overlying dye, but not the underlying scorch. These are early days, and the odds against getting a result are slim if the "ghost" image is one that is age-related or depends on lots of other things coming together in the correct sequence. Nothing ventured, nothing gained.

Update:14th March

The new line of experimentation is underway.

The dye is a boiling water extract of pomegranate rinds (rich in tannins, gallates etc).Used on its own it gives linen a yellow-brown to orange colour (top left)  When used on alum-mordanted linen one gets a greyish-green colour (top right).

Most but not all the dye can be bleached out with hypochlorite solution.  Interestingly there's a faint brown remnant that tends to be more intense on the alum pre-treated side. It may or may not be relevant to the Turin Shroud, these being early days.

 Another result (today's):

 Top (inside yellow box): a wet imprint from a brass crucifix that has been painted with a syrup from boiled/semi-evaporated pomegranate rind extract almost to dryness, after (a) conversion to negative image and (b) 3D enhancement in ImageJ.

Bottom (inside blue box): the dry imprint obtained/reported many months ago  by pressing the same crucifix (heated) into linen. It was not my best scorch imprint (much of the face being invisible) but was chosen for a preliminary rough comparison between rival wet and dry imprinting technologies.).

See the banner at the top of my specialist Shroud blog for other scorch results obtained from the same crucifix template.

New result in the pipeline- might it be THE answer to the "enigma" of the Shroud?  

I shall keep it under wraps for now, there being some controls that need to be done. One should not count chickens I know, but if all goes well, the title to the next posting might well be this:

Is the Shroud of Turin a ghost image – the original dye imprint having been lost to expose a previously hidden - albeit faint -  dye-mordant underlay?

Update Sunday March 15th

I need a name to describe my new modelling of the Shroud image  (inspired by Joseph Accetta) using an alternative to his iron/oak gall ink. Mine uses alum-mordanted concentrated aqueous extract of pomegranate rind deployed  not as ink, this syrup being deployed as a kind of  natural sticky “paint”. However, let’s make one thing abundantly clear. The pomegranate extract was NOT used to paint a free hand image (this blogger does NOT subscribe to the Charles Freeman strand of thought that blithely ignores the Shroud's negative image). The home-made pomegranate paint was applied to a 3D template that was then pressed down into linen to leave a NEGATIVE imprint, with no brush strokes, no directionality of any kind, and which responded after a fashion to 3D-enhancement in ImageJ, as expected of any image, good bad or indifferent,  that displays pigment density differences.

Some images will follow later in the day, showing essential steps in the new technique, which is simply offered as a model system (as was my contact scorch modelling) to show how certain key Shroud image characteristics can/may be reproduced, at least in part, with no claim that the chemicals and/or procedures used were the actual ones (That we may never know, not unless a previously lost or concealed 'tell all' manuscript were to emerge from some dusty14th century archive).

Provisionally. let's call it the AMPS -imprinted model (AMPS = Alum-Mordanted Pomegranate Syrup).

Brief summary of the AMPS technique:

1. Prepare syrupy concentrate from boiled pomegranate rind.

2. Paint syrup onto template (am using same brass crucifix as used previously for scorch imprinting).

3. Imprint left by pomegranate syrup on linen, the latter having first been impregnated with alum mordant.
Here's the imprint after washing and drying to remove unbound syrup. It's turned grey-green! Well, I did say it was a model system. The mordant has certainly done its job.

It's a simple matter to turn that green image into a more authentic-looking sepia using oxidising agents. Hypochlorite ("bleach!") worked instantly - tested above the waistline. Hydrogen peroxide works slowly after a fashion (below waistline). Yes, the model system is I grant you  being tested to its limits.

Was the alum essential?

Left: before washing. Right:after washing. The top image is the pomegranate imprint, without alum-mordanting. The lower is a contact scorch from a previous experiment with the same crucifix.

In fact, the alum was not essential, at least not for surviving a single wash with warm tap water. In other words, my pomegranate extract is a powerful dye in its own right, without alum assistance (it having been chosen after an internet search for natural dyestuffs). However, one cannot be certain that the fabricators of the Shroud image had used a dye that was so effective without a mordant. Alternatively, it's interesting to know that the TS image could in principle have been made without use of alum, should it be found there is little or no detectable aluminium in the image areas - the latter being still a contentious point, as discussed previously in connection with the known limitations of STURP's x-ray fluorescence to detect elements of low (less than 17) atomic number.

It's all to easy to start with a model, and then acquire unexpected results that distract from the initial ideas. Here's a case in point. The idea of a 'ghost image' under a dye-mordant combination, generated by slow release of sulphuric acid from the mordant, is being lost sight of. Why? Because it was orignally intended that bleach could be used to decolorise dye-mordant, exposing a 'chemical scorch'. But the bleach has acted different from expected - it's converted the green mordant-dye combination to a very intense sepia image that cannot (surely?) be a ghost image, but an oxidation product that is highly coloured, not "bleached". 

This seems a good time to break off, and carefully review the results so far against initial assumptions and predictions.  

Back again: that result with the bleach looked wrong somehow, and indeed probably was: insufficient bleach added. Am now getting almost complete bleaching of the pomegranate syrup imprint, with or without alum, when excess bleach is dripped on and allowed to do its thing for a few minutes. That  means the show is back on the road.  Here's a rough outline of the protocol for further experimentation, aimed at testing the alum-derived H2SO4 model:

1.  Imprint with pomegranate syrup onto alum-impregnated cloth.  That would represent the Mark 1 Shroud image - big and bold, almost certainly with reverse-side action as well, even with viscosity-increasing additives as proposed by Joseph Accetta. But that doesn't matter greatly if it's the dispensable Mark 1 image.

2. One then has to model the effect of ageing, wear and tear on that Mark 1 image, which would result in the flaking off of much of the image, and to fading of the colour due to exposure to light and oxygen (while all the while the alum is releasing sulphuric acid into the linen out of sight underneath the dye imprint). How can it be modelled? That's the difficult and uncertain part, but exposure to light and oxygen at slightly elevated temperaure for days or weeks even, with or without water vapour, might be the way to go.

3. At some stage it will then be necessary to see what is under the remaining dye/mordant stain. The latter will be taken of with an excess of hypochlorite bleach, but the latter will (I maintain) NOT bleach any "scorch" produced by sulphuric acid if as I suspect it behaves like a heat scorch, and is chemically-dehydrated carbohydrate as per STURP summary. So what one looks for is a ghost Mark 2 scorch image, faint sepia in colour, stubbornly remaining after bleach treatment, probably (hopefully) with no reverse-side discoloration. It would also be interesting to check out any remaining Mark 2 scorch image under a uv lamp. If it behaves like the "etched-on" model images produced by Luigi Garlaschelli with his acidified metal oxide slurries, it too will be non-fluorescent, matching yet another of the (alleged) properties of the TS image.

Update: Monday March 16

Interestingly, there's a parallel chemical system to that of alum  with its Al2(SO4)3 as "active ingredient".  It's based on iron(III) sulphate, Fe2(SO4)3. The resemblance is close (both their solutions being strongly acidic, due to hydrolysis to sulphuric acid).

Indeed, it may be that everything that has been attributed so far to alum mordant producing sulphuric acid and a ghost image may in fact be due to an iron-based mordant action instead.  If that were the case it would allow one to make some inferences that could resolve the 'unfinished business' re Walter McCrone's focus on traces of 'too pure' iron oxide on the Shroud.

I shall now take a break while assembling an iron dossier. Be prepared for a further instalment in due course on what might loosely be termed the non-thermal scorch hypothesis, mediated by slow-acting sulphuric acid substituting for hot metal template as a chemical dehydrating agent,  and derived from hydrolysis of alum OR iron(III) sulphate.

Al2(SO4)3 + 6H2O  ->  2Al(OH)3 + 3H2SO4


Fe2(SO4)3 + 6H2O ->  2Fe(OH)3 + 3H2SO4

Note: either of the two hydroxides can easily rearrange to make the hydrated oxides, like, er. McCrone's iron oxide, accommodated within a "painted image" scenario. (Did he ever consider dyeing, as distinct from painting?).

In fact, there may not really be "iron(III)hydroxide"  (Fe+++ 3OH-) as generally written.

It's more correctly written as a hydrated mixed oxide/hydroxide:   Fe+++ (O--) (OH-) .H2O.

See the wiki entry for that interestingly revisionist version!

Speaking of which - dyeing that is -  the so-called "dye-rot" that degrades some ancient printed textiles has been attributed to iron-based mordants, especially those that use iron sulphates, as distinct from iron chlorides (sulphuric acid being non-volatile, unlike hydrochloric). 

Note the current focus on dyeing,  with initially soluble pigments, as distinct from painting with insoluble ones. Hat tip again to Joseph Accetta, assuming the problem of reverse-side (aka obverse-side) action can be resolved. If it can't, this blogger may need to revert to instant thermal scorching. For now, it's sufficient to flag up that difficulty, pointing out that penetration of a Mark 1 dye stain to the opposite side would not matter if it had now completely disappeared.What matters is the hypothesized Mark 2 ghost image. It's not inconceivable that it would be restricted to the top surface only, i.e. to the most superficial parts of the linen fibres in contact with the Mark1 dye-mordant combination.

Update Tuesday March 17

Extracts from new pomegranate. The tray on left has boiled concentrated extract from rind and pith only (not seeds). The one on right with the greenish tinge has added alum (potassium aluminium sulphate).

The two extracts have been imprinted onto linen offcuts for long term storage. The aim is to see if ghost images appear due to chemical dehydration of superficial linen fibres, mediated perhaps by alum-derived sulphuric acid.

Concentrated syrups were made so as to produce a paint-like consistency without external aids.The 'paint' has been used to imprint from a bas relief template.  However, an order has been placed for gum arabic (viscous solution in water) so as to allow that option to be explored, although there is then an alternative target for the sulphuric acid that might reduce effects on the linen carbohydrates.

Update Wednesday 18th March

J. Accetta's dye-imprinting idea, or dare one say paradigm, and my response to it here, is currently the subject of a posting on Dan Porter's shroudstory site. I've responded to the splendid David Goulet, but decided to exit as soon as the ad hom tendency made its inevitable appearance.

Invoking Occam's razor (entities should not be multiplied unnecessarily) is always a cheap shot employed by those who cannot bother to get acquainted with new thinking, who wish to to preemptively dismiss not just the research but the researcher.

In fact there's scarcely any grounds for invoking  Occam's razor right now. The dye-imprinting idea is Accetta's, not mine. All I have done is to focus on a particular aspect of medieval dyeing - the recourse to mordants that release sulphuric acid - and to link that to STURP's 1981 Summary. There we were told that the image had the chemical and spectral characteristics of chemically-dehydrated carbohydrates, and sulphuric acid was indeed specifically mentioned as an agent capable of dehydrating. 

 Quote (STURP 1981) : The scientific consensus is that the image was produced by something which resulted in oxidation, dehydration and conjugation of the polysaccharide structure of the microfibrils of the linen itself. Such changes can be duplicated in the laboratory by certain chemical and physical processes. A similar type of change in linen can be obtained by sulfuric acid or heat. However, there are no chemical or physical methods known which can account for the totality of the image, nor can any combination of physical, chemical, biological or medical circumstances explain the image adequately.

All I have done is marry together the STURP 1981  Summary with STURP's Joseph Accetta (St.Louis 2014) to get what I consider a coherent narrative, and am now in the process of designing experiments to test the hypothesis. Suggestions that this blogger/retired science bod is an innocent abroad, 'multiplying entities unnecessarily', coming as they do from someone who acknowledges he hasn't read one's postings in full, are hardly calculated to impress, especially when there's so much work needing to be done, and all at my own expense needless to say.  Speaking of which: today I must place orders for iron sulphates. I shall play safe, and acquire both iron (II) aka ferrous sulphate and iron (III) aka ferric sulphate. Stocks of high quality linen also need replenishing.

Speaking of the shroudstory site, it was there that some of us had our first glimpse of what Joseph Accetta intended to say at the St.Louis conference in October the same year.

Here's a comment I attached to that posting. Note the singling out of sulphuric acid as (possibly) the crucial ingredient:

June 5, 2014 at 12:55 pm
Try downloading this PowerPoint presentation from Joseph Accetta, David (he being the subject of a recent posting here, and one of STURP’s genuinely scientific, non-agenda driven, non grandstanding participants in my view).
(Unzip as if a pdf).

Go to the last few pages (approx 24/25). There you will see model spectroscopic (ir) studies not just with thermally-imprinted scorches, but also with linen that has been chemically dehydrated with 36% H2SO4 and even your invisible ink (lemon juice).

I’d be the first to admit there may be little to distinguish between an image produced by chemical as distinct from thermal dehydration (especially if chemical action was heat-assisted – see Luigi Garlaschelli’s model ‘frottage’ imprinting with acid-contaminated red iron oxide). It’s the vehicle for acid that is important (not too runny, not too viscous).
Some of us eagerly await details of what JA will say at St.Louis. Let’s hope it receives more attention than his meticulous and detailed studies to date.
Nuff said. I’m thinking of doing a post dedicated entirely to JA (he being my kind of scientist).

Update, still 18 March

David Goulet reminded me yesterday of an exchange we had in mid-January on  a shroudstory posting on Accetta's dye-imprinting. As can be seen, this blogger was making no secret of his scepticism as little as 2 months ago!

January 14, 2015 at 9:41 am
So the bas relief theory but using a woodprint? And the mechanism of image formation to the cloth?

January 14, 2015 at 10:22 am
It’s a wet method that’s being proposed, David, based on ancient recipes for printing ink (iron gallate, gallic acid being trihydroxybenzoic acid, a natural plant-derived product). While simpler, less fiddly in practice than scorch-imprinting off a hot template, it’s going to be harder obviously to tick all the boxes re superficiality, lack of colour penetration etc.
If a woodprint had been used as template, would it not have been possible to get a more realistic differentiation, say between hair and skin?
My money’s still on thermal imprinting off a bas relief or 3D template(s.) Most of those who say it fails to match this or that feature of the TS have never done a scorch imprint in their lives, and/or don’t wish to know about the subtle effects that are achievable with relatively small changes in technology. Dry, e.g. thermal imprinting, maybe with chemically-sensitized linen, gives a far more predictable outcome. What’s more, it can chemically /permanently modify the most superficial fibres of the linen. It beats simply sticking something to them that can subsequently drop off (or be claimed without a shred of evidence to have done so, leaving, as if by magic, chemically modified fibres, ghost images still with 3D properties etc!).

January 14, 2015 at 10:33 am
Thanks for the summary, Colin. Agreed, the woodprint/wet theory has some major hurdles to overcome.

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