Was this the man who supplied the chemical know-how for faking the Turin Shroud - 13th century Paul of Taranto?

Update 30 June 2015  Looking back through my older postings, I came across this one. Folk may be puzzled by the abrupt switch from sulphuric to nitric acid with no reasons being given. That's because I had been using the Comments facility on a different site to hint at a rapid sea change in thinking.

The caption reads: "Paul of Taranto was a 13th century Franciscan alchemist and author from southern Italy. Perhaps the most recognized of his works is his Theorica et practica, which defends alchemical principles by describing the theoretical and practical reasoning behind it. There is also evidence to suggest, however, that Paul is also the author of the much more widely known alchemical text Summa perfectionis, generally attributed to Geber (aka "Pseudo-Geber")

Here's the first known recipe (in precise detail) for making nitric acid fumes (which might, just might, have been used to produce the Shroud image via its propensity to oxidize and 'nitrate' (verb) organic matter, turning it sepia or yellow-coloured in the process).

"Take a pound of Cyprus vitriol, a pound and a half of Saltpetre, and a quarter of a pound of alum. Submit the whole to distillation, in order to withdraw a liquor which has a high solvent action. The dissolving power of the acid is greatly augmented if it be mixed with some sal ammoniac, for it will then dissolve gold, silver and sulphur"

Cyprus vitriol is copper sulphate, saltpetre is potassium nitrate, and alum is potassium aluminium sulphate. (Sal ammoniac is ammonium chloride, but is not needed to generate nitric acid).

Here's a mechanism that has been proposed for what happens when a simpler binary mixture of copper sulphate(CuSO4) and  potassium nitrate (KNO3) is heated to a high temperature (600 degrees C or higher). The chief end product, nitric acid, is shown in red ( HNO3)

2CuSO4  → 2 CuO + 2SO2 + O 2  

KNO3 + SO2 → KO3SONO

2 KO3SONO → N2O3     + K2SO 4  + SO3

If the cooling is insufficient, N2O3  decomposes spontaneously:

N2O3  →  NO + NO2

or otherwise reacts with water:

 N2O3  + H2O  → 2HNO2

and the subsequent disproportionation of HNO2  produces HNO3 :

3HNO2  →  HNO3  + 2NO + H2 O

 

Oxygen produced in the first reaction oxidizes NO:

2NO + O2  →  2NO2

and the dissolution of the resulting oxide in water yields further nitric acid:

4NO2  + 2H2 O + O2  →  4HNO3

 These days the reaction is accomplished faster and more easily by heating a mixture of potassium nitrate and concentrated sulphuric acid, H2SO4, in a glass retort, or other all-glass apparatus, i.e. no corks, rubber bungs or other organic matter.

The nitric acid collects as a liquid in the cooled receiving flask on the right. It will be yellow or brown due to dissolved nitrogen dioxide (an impurity). There may be other oxides of nitrogen too (thus the references to NOx to avoid being too specific)

So what's this got to do with the Turin Shroud? 

 I propose that the Turin Shroud  image may have been formed by a reaction between nitric acid and/or nitrogen oxides (NOx) acting upon organic matter, notably carbohydrates (oxidation) and even protein (nitration). It may even account for the blood that is "too red".

I provisionally call it the HNO3/NOx fumigation theory.You read it here first, correction - second. I dropped some hints yesterday on shroudstory.com. (See later comments). The key concept is that of fumigation, note, with relatively little liquid water. Details to follow in the next days and weeks (nitric acid  is on order for a new round of acid experimentation, close on the heels on my H2SO4 mini-project - see the posting immediately preceding this one)

Methinks that'll do for now. I'll give details in future postings, and suggest how the hypothesis can account for a considerable number of Shroud characteristics (the latter collectively earning it the description "enigmatic") and potentially be tested, possibly  falsified. Please note: it's just a hypothesis for now: my interest is less to do with debunking the authenticity of the Shroud, and more to do with trashing the absurd notion that the Shroud HAS to be of supernatural origin. See that woeful article in the Independent, December 2011, the one that prompted this blogger/retired biomedical scientist to go 'mixing it' with the purveyors of pseudo-science.

Further reading:

On Pseudo-Geber/Paul of Taranto: preview of  William R.Newman's critique: 

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What does sulphuric acid do to linen fibres? Might it provide us with clues to the Turin Shroud?

Introduction and Summary: It was supposed initially to be a pot-boiler of a posting, describing what a strong solution of sulphuric acid (H2SO4) i.e. "battery acid" does to linen when it becomes more concentrated by slow unaided evaporation.  I needed to know in order to evaluate a current hypothesis regarding the Shroud of Turin and its 'enigmatic' image.

 It then turned into something different - and hopefully more significant - when I found  different results with cotton from those with linen, and began doing some reading (including my own half-forgotten postings from as long as two years ago).

I shall stick with the original idea of showing the results of my experiments in a series of photographs - that being the raison d'etre of this site - to allow the reader to see things through the eyes of a retired researcher - albeit  one who makes no claims to experimental sophistication, restricted as he is to a kitchen (or in this case garage) laboratory, dependent on internet suppliers for chemicals etc.  But here first is a short summary for the benefit of those who simply want a take-away message:

Summary: evaporation of initially approx 35% sulphuric acid, H2SO4, on white linen resulted after 2 days or more in loss of mechanical strength, with only slight darkening of the fabric. A cotton sample similarly treated retained its colour and mechanical strength. The difference may be due to the presence in the central  cores of linen fibres (secondary cell wall) of appreciable amounts of hemicelluloses that are more chemically reactive than cellulose and essentially absent from cotton.

These results raise the possibility that the difference between the Turin Shroud's coloured image v non-image fibres are NOT confined to the highly superficial primary cell wall (estimated 200-600nm thickness) and may extend to the central core of the fibres too, resulting in loss of physical and chemical integrity, explaining perhaps the relative mechanical weakness of image fibres reported by STURP's Raymond N.Rogers in his sticky tape sampling. If so, the process that gave rise to image imprinting on the TS may not have been as subtle as previously claimed, making it possible perhaps to model using technology that was available in the 14th century, corresponding to the radiocarbon dating.

Now for the experimental details:

The label says it's "100% linen". It's about to be cut into strips.

Strip cut away, with handy ribs that act as guidelines for what follows

The strip has been used to make the chemical formula for sulphuric acid. The cable ties are for dipping in battery acid (see unopened container in background).

Here's a close-up. It states the specific gravity. One has to assume it's the standard concentration for battery acid (usually around 35% H2SO4)

Here's a long-shot of the experiment set up in the garage. Note the polyethylene box to contain any spills.

Ready for dipping in acid

The cotton shown here is being used as a support only. The linen cut outs are to be dipped in the battery acid (see shallow dish with skull and crossbones).

Here's the O of H2SO4 in the acid, with attached cable tie

Laying out the formula on the cotton support after dipping in acid.

Formula complete. Now all we have to do is wait.

Here we are two days later, and at first sight there appears to be no obvious change. But beware. Those letters still feel damp (wash hands immediately after doing a touch test). Water controls dry out in less than 2 days.

Look more closely, and one sees there is a change. for a start the treated linen is now a light beige colour, while the untreated control  (removed centre of the O) is the original white.

Here's visual proof that the linen is still wet. It's translucent. Note how one can see the red tape through the treated linen but not the untreated control. That linen is a biohazard needless to say (kept well away from other occupants of the house).

Here one can see clearly the beige colour of the acid-treated linen against the original linen shirt.

Here's a supplementary test that was most revealing. The "2" of H2SO4 has been placed on a hot radiator (which will be wiped with bicarbonate later to neutralise acid contamination).

The "2" quickly darkens still further at the higher temperature. Note the difference between it and  untreated linen.

When the heated "2" was replaced, something unexpected happened. When trying to position it correctly, it fell apart!

Here's the same against the same original black background. Gentle prodding with a pencil showed that all the linen was now highly fragile, while still relatively "white" (something of a surprise).

Here's the fragmented "O" with untreated control. The colour change is subtle, but there's no doubting that the acid has seriously degraded the linen while not greatly altering its appearance.

What I haven't said is that two squares of cotton fabric were also steeped in the same battery acid, and also exposed to air for the same period. Surprise finding: they not only looked the same as untreated cotton (no surprise, in view of above) but seemed just as strong as the original cotton. They could be stretched with maximum force and did not tear!

Why should that be? Why should linen be chemically attacked by  H2SO4, of concentration intermediate between battery acid and conc.H2SO4 (after evaporation of some water) but not cotton?

The original purpose of the experiment was to test the hypothesis that sepia Shroud image might have been formed from dye mordants (alum, iron sulphates) releasing sulphuric acid into the fibres of the linen which on evaporation of water produced local high concentrations of H2SO4 leading to discoloration of the cloth. That hypothesis was NOT confirmed in these experiments with actual high strength H2SO4. Instead there was a totally unexpected finding that linen differs from cotton in being highly susceptible in some way to acid, losing its tensile strength,and indeed disintegrating under light tension. Why? Might that finding have something to say about the nature of the TS image?

Hypothesis

Firstly: can the difference between linen and cotton be rationalized. Yes. I believe it can. Cotton is well known as the purest source of cellulose in nature (the figure generally quoted is 90%). Cellulose is celebrated for its resistance to chemical attack (being made use of in chemical laboratories for filter paper able to withstand a wide range of harsh reagents). Cotton contains virtually no hemicelluloses, which despite their name have virtually nothing in common with cellulose. Hemicelluloses are chemically far more reactive than cellulose.

Now let's consider linen, or the bast fibres from the stem of flax plants from which it is derived. Linen is generally quoted as having 5-15% of polysaccharides that are NOT cellulose, comprising mainly hemicelluloses and pectins.

 Late addition: a literature source found by googling (linen hemicellulose) that confirms the major difference regarding linen and cotton re the major difference re hemicellulose content.

 (References to detailed carbohydrate compositions have proved elusive, but if I find any more, I'll add them here).


Like: this passage from Caspar von Uffhofen in 'The Mystery of the Shroud"

Linen yarn is quoted above as having 11-17% hemicellulose, and a mere 1.8% pectin. How strange that the hemicellulose of linen is rarely if ever mentioned in Shroud image literature, especially as cellulose is chemically so inert by comparison. Some sources, naming no names, discuss linen as though it were 100% cellulose. I have even seen the hemicellulose referred to as "an impurity"

A general description of flax fibres is that they comprise a cellulose-hemicellulose cross-linked combination embedded in a gel matrix of pectins (though some perhaps most of the pectin is lost when flax fibres are retted to make linen).

The presence of hemicelluloses could explain why linen is greatly weakened by sulphuric acid, whereas  cotton is not. What's more the acid must affect the entire fibre to account for mechanical weakening - not just the most superficial part of the fibre. Those reading this who are familiar with the literature on the Turin Shroud image will no doubt be aware of where this is all leading.

Here's an image I showed in a posting over 2 years ago on my specialist Shroud site:

The core of a linen fibre is not purely unreactive cellulose. There are reactive hemicelluloses there too that are susceptible to thermal or chemical change without (perhaps) becoming highly coloured, due to dilution effect of unaltered cellulose.

In fact, i returned to the same theme again and again a year later. See this one in particualr entitled: Why are Shroud image fibres mechanically weaker than non-image bearing fibres? Pyrolysis of core hemicelluloses?

My proposal that core hemicelluloses might have a role to play in explaining the weakness of Shroud image fibres sadly failed to attract attention elsewhere. Maybe it didn't fit with the prevailing narrative that the Shroud image and associated chemical modification is entirely confined to the most superficial part of the linen fibre, typically quoted as 200nm thick, and that absence of colour in the core of the fibre means there has been no physical or chemical change there (despite the mechanical weakness of TS image fibres discovered by Raymond N.Rogers in his 'sticky tape' sampling of TS fibres, relative to non-image fibres). Or maybe it was the tying of the core susceptibility idea to the scorch hypothesis that guaranteed that even if seen and commented upon, it would be quickly dismissed and forgotten.

Takeaway message? Too much emphasis has been placed on visual coloration in image fibres, as if chemical changes to flax or linen carbohydrates always produce a yellow colour. That's led to the paradigm that the Shroud image is incredibly superficial and so, ipso facto, the totality of physical and chemical changes must also be restricted entirely  to the most superficial part of the fibre, corresponding roughly with the primary cell wall. One simply cannot make that assumption, given that chemical change, sufficient to weaken fibres, need not be accompanied by a handy self-indicating colour change. Example from this posting: there was only a slight darkening of linen fibres when exposed to sulphuric acid despite massive weakening of fibre tensile strength, but only in linen - not cotton. So who's to say that the process that produced the image on the TS was not - as is generally maintained -  one that was too subtle to be explained by conventional physics or chemistry, and was instead  one that degraded linen fibres, notably the core hemicelluloses, producing major changes at the chemical and mechanical level, but ones that are not obvious under the microscope?

There is every reason to put the uv excimer lasers away, at least for now, and consider all the various ways in which a medieval artisan might have set about imprinting an image onto linen, one that he and his masters could claim was that left on Joseph of Arimathea's linen.


Update: here's a comment I posted earlier to shroudstory.com, essentially addressing the point raised here - namely changes to SCW on image capture that are maybe not as visible as those to the superficial PCW:

Colin Berry

April 1, 2015 at 4:30 am

Reply

Forgive my saying, Piero, but you are making the same error as Paolo Di Lazzaro and his ENEA colleagues in assuming that because the TS image COLOUR is superficial, confined (maybe) to the PCW or a Rogers’ type coating, then ipso facto there are no changes to less superficial parts of the fibre.
Are you not forgetting something? Image fibres are weaker than non-image fibres. That was shown by the ease with which they could break off and stick to Rogers’ Mylar adhesive tape. It would take more than changes in the PCW – an ultra- thin skin on a much thicker mainly SCW fibre – to render the entire fibre brittle and prone to fracture. (Let’s not forget that the Mylar initially stripped off entire fibres – not image “ghosts” – the latter not being seen/inferred until image fibres were subsequently pulled away from the tape).
Try by all means to get the Vatican to consider your AFM scanning. But let’s dispense with the notion that the imaging process affected only the most superficial parts of the fibre. The core of a linen fibre is not entirely crystalline cellulose. There are significant amounts of hemicelluloses and pectins there too – the so-called non-cellulosic polysaccharides (NCPs).Their physical and/or chemical disruption could compromise the strength and integrity of the entire fibre. Being in a minority relative to cellulose microfibrils means that changes to those NCPs might not be so readily visible as coloration, which is where we came in.

Update: Thursday 2nd April

Here's a schematic diagram found by internet search that shows the inferred relationship between cellulose microfibrils and hemicellulose crosslinking 'bracing'. (It's part of a discussion of expandable primary cell walls but there's every reason to suppose that it applies equally well to the secondary cell wall, despite the PCW and SCW fulfilling different roles at different points in the plant cell's life history).

Note that the bonding between cellulose and hemicellulose is not via permanent covalent chemical bonds. It's via hydrogen bonds, the weaker nature of which (individually) can be more than compensated by their numbers. The crucial difference where susceptibility to thermal and chemical treatments are concerned is that it's relatively easy to break hydrogen bonds which may or may not subsequently return to their original geometry. So we have here a possible mechanism by which  image imprinting could seriously impair the tensile strength of linen image fibres  without producing colour, and without affecting cellulose crystallinity, the latter inferred by Rogers from unaltered birefringence pattern under crossed-polaroids,. There's an analogy that can be made with double-stranded DNA, the two strands of which are held together in the double helix via hydrogen-bonding between base pairs. Once can separate the stands by heating and "melting". However, to get them to return to their original correctly base-paired configuration one has to "anneal",  ie. cool very slowly, which allows the separated strands  to 'experiment' with different arrangement until the optimum most-stable pattern is restored.

Conclusion: imprinting linen with a superficial image using one or other technology may not result in visible change to the inner core, but that does not preclude serious disruption occurring at the molecular level that may not be visible either to the unaided eye or under the microscope. In short: superficiality of visible coloration does not necessarily mean that the input energy was of an exceptionally subliminal kind (e.g. high energy/short pulse) unknown to science. Maybe Shroud image fibres are more seriously compromised than their faint yellow colour would indicate. Their mechanical weakness is the clue to more profound physical or chemical disruption having occurred within the SCW cores of the fibres. Maybe medieval technology was capable of producing that particular presentation known to paramedics of  minor superficial change concealing more serious 'internal injury'.

Further update: have just this minute googled (shroud turin image fibres weaker):

Am I the only one to consider that altered mechanical strength to be an important pointer to change at the molecular level (as important, if not more so, as change in visible colour, reflectance spectrum, uv fluorescence, dichroism under crossed polaroids etc etc)? Yup, the first 6 listings above are all to my own postings (but then I have been muttering about fragile SCW hemicelluloses for well over two years now).

Technical footnote regarding different grades of sulphuric acid

The so-called "concentrated sulphuric acid" is purchased as a dense oily liquid, which is 98% H2SO4, 2% H2O.  It is highly dangerous, and not the sort of chemical one wants around the house or even garage. It's to do with its avidity (old-fashioned chemical term) for water. One gets a hint if one dilutes it with water following the safe and correct technique, which is add the con acid in a thin stream to water with constant stirring.  The temperature rises quickly (one may see steam) and one may hear a rumbling sound  (from cavitating steam bubbles). Never ever imagine one can dilute by adding water to conc H2SO4. Try doing that and the whole lot is liable to come back in your eyes and face in short order: hot sulphuric acid is not to be recommended. Why the projectile event?  Because of density differences the water initially sits on top of the denser H2SO4. There's then the violent heat of dilution at the interface that then causes greater contact, more heat, more contact etc etc, and steam propulsion out the beaker does the rest. This blogger was once a few yards from a lab technician who did it the wrong way (I blame the researcher who failed to enquire ahead of time as to the level of her chemical -handling credentials). Fortunately no permanent injuries resulted, but there was a lot of unpleasant clean up and neutralisation (sodium bicarbonate) to be done of splattered acid - over bench surfaces, reagent bottles, lab notes and lab coats.

I shall return shortly to discuss what happens when conc. sulphuric acid is allowed to stand (in a safe place) exposed to moist air, and compare with the experiment described above when pre-diluted acid of battery strength (approx. 35%) is similarly exposed.

Back again. Yes, it's not hard to find references to the volume increase that is seen when conc.H2SO4 is exposed to air, and neither is it difficult to find references to solutions of dilute(d) sulphuric acid becoming more concentrated as they evaporate and shrink in volume. What I have not been able to find thus far is quantitative data. One would like to know the final concentration of sulphuric acid after conc.H2SO4 has picked up the maximum amount of water vapour, and conversely the final concentration of H2SO4 after the dilute acid has evaporated to its maximum concentration of H2SO4. One assumes the two acids - conc. and dilute-  converge to the same figure for a given atmospheric moisture content. It's obviously somewhere between 35% and 98%, but I have no information on whether it's nearer 50% or 90%. However- one things for certain: the concentration never reaches 98% for physical reasons, due to the aforementioned hygroscopic nature of 98% H2SO4, and never acquires the ability to cause rapid charring of fabric, as seen when it is treated with conc.(98%) H2So4, recalling the findings above of at best a faint beige color on standing for 2 days in air (with non-evaporated liquid still visible).

Reminder from a previous posting here on what can happen when fabric is treated with conc.(98%) H2SO4.

Final addition: what about the initial hypothesis - namely that traces of sulphuric acid from mordants may have caramelized the linen to produce the TS image we see today(maybe as a ghost). Well, there was a very slight colouring of the linen exposed to H2SO4 over 2 days, more beige than yellow or sepia, but hardly enough one would think to account for the TS image, faint though it is. If a high concentration of H2SO4 on its own cannot produce a reasonably visible sepia coloration, then it's unlikely that trace amounts can do so, unless one invokes catalysis from other constituents (Occam's Razor!).

Never mind. The H2SO4 hypothesis has led me to consider another chemical scenario that is not too far removed from H2SO4,  and one moreover that would seem to tick a lot of boxes, even the tricky ones like ultra-superficiality/confinement of image to the PCW, half-tone effect, bleaching with diimide, even Adler and Heller's "blood-first" conclusion that has always been an Achilles heel for  a medieval provenance.

So what's the new idea? Be patient, folks. It will be the subject of my  next posting, arriving in the next few days.

Nope, this is the final addition, added Friday 24th April, some 3 weeks and 5 postings after the one above.  It's my response to the ludicrous accusation (same old, same old) from the Usual Suspect on Dan Porter's shroudstory site that I have "recycled" his ideas. The crucial word is "fumigation". No sooner had I hit on the idea that HNO3 vapour (as distinct from liquid solution) might be less problematical as a chemical developing agent than I quickly adopted the term "fumigation". What are the one-word alternatives? I can't think of any off the top of my head, and fumigation is easy to understand. But the usual suspect has also used that term, albeit in an entirely different pro-authenticity context for post-mortem imaging in a 1st century tomb that was carried out, he claims, according to a complex routine (I shall spare readers what for me is eye-glazing detail), and in any case has never been put his model to the experimental test, the relying he says on "thought experiments".

Anyway, just to let folk know that I  was doing some house-keeping in my work area today, and came across this note that I wrote to myself, almost certainly in the first few days of April when I realized I had reached the end of the road with sulphuric acid, and was wondering where to go from there:


Here it is verbatim, faulty punctuation, crossings-out an' all, but no deployment of the f word at this stage.

"Time for a total rethink on the TS image. Maybe there is was a gas or vapour exposure. Acid gas: to explain weakening of fibres - prob by acting on SCW hemicelluloses. Action of acid gas in non-image areas as well. Some kind of target molecule but few lower density?  Protein.  Relatively few acid gases. /vapours  HNO3 - has a lot going for it."

Can that weird and wonderful Turin Shroud be modelled? See my hands-on results with dye-imprinting, reported in real time.

For background, see the posting immediately preceding this one. It attempts to explain my switch in focus from the 'scorch' model to that proposed last year by Joseph Accetta - based on medieval dye imprinting technology. I've extended and embellished it a bit, but as the title indicates, this post is about getting 'hands-on' experience with dye impriinting off 3D templates, with a view to getting familiar with the pros and cons of the Accetta model, vis-vis the scorch model.

I'll be posting photographs of what I'm doing over the next few days, interspersed with practical details and interpretation. (Beware: I've been accused today of being hopelessly  biased, a "hostile witness", forcing me to explain yet again the scientific modus operandi, based on model building, model testing and model refinement. My answer to that? Always keep in mind the motto of the UK's Royal Society: "Nullius in verba" (take nobody's word for it), least of all mine. It's the ideas that count, the design of the experiments to test them, the presentation and interpretation of data.

Here's a photograph from my own research archive to get the ball rolling:

Scorch v dye imprint off a brass crucifix

That's a scorch imprint on the left, one I reported here on November 25 last year. Yes, it responds beautifully to light/dark inversion and 3D-rendering, as per Turin Shroud. But I've been moving away from scorching, for reasons discussed earlier (cumbersome technology, lack of a persuasive historical rationale, unless substantive evidence can be found to lend further credence to my  2012 "roasted Templar" hypothesis).

(As i've said previously, it was the Machy mould for a Lirey Pilgrims' badge, circa 1357, that led me to suspect that the Mark 1 shroud was fabricated to appear as though an ancient sweat (and blood) IMPRINT - thus the negative photograph-like character - making wet technology based on dyes or other liquids more probable that dry thermal imprinting).

Say hello to an alternative technology - the  one proposed by Joseph Accetta last year, (pdf file) involving dye or ink imprinting off a woodcut block. I don't have access to engraved woodblocks, but do have that same brass crucifix. And while Accetta's imprint medium focused on medieval  'oak gall ink', a tannin-rich extract with added iron salts, I've substituted a tannin-rich extract from pomegranate (rind and peel). That's the imprint on the right.

I've been ringing all kinds of changes on the technology - incorporating mordants that assist attachment of dye to cloth, incorporating iron salts to convert tannin dyes to dark inks, using terracotta templates moulded from soft clay instead of metal.  Results will appear here in the next few days.

Monday March 30th

As I say, one of the appealing aspects of Joseph Accetta's dye-imprinting model is the nature of the template. It can be made from wood, by a combination of carving and sanding technique. (Quite where "engraving" enters the picture, if at all, is something this blogger is still pondering). Might the technology have been even simpler? Might the template have been moulded from something of which Nature supplies an abundance - clay? That was the  first question I wished to address, and here are the preliminary results:

All ready to do first imprinting from a clay template right. In the backgroud: a pomegranate, used to make tannin concentrate (in orange pot). Previously-used brass crucifix for size comparison.

Close-up of template. It's crude admittedly, was moulded using a photo of one of those ancient Chinese terracotta warriors as model (not the Man on the Shroud!).  What you see is after air drying, baking in a fan oven at 180 degrees C, and then varnishing with gum arabic, about which more later.

The 'LOTTO' configuration was used for dye imprinting (Linen On Top, then Overlay). The varnished template was painted with pomegranate extract and linen laid on top as shown. Note the bleed-though (at first sight a disadvantage of wet imprinting, but this is a modelling of the Mark 1 imprint - see preceding post for thoughts re a "ghost" Mark 2 image surviving on today's Turin Shroud.

Peeling back the linen to reveal negative dye imprint.

Here's the result of imprinting onto linen that has been pre-mordanted with alum.(I'll enlarge further on the pros and cons of different mordanting strategies later).

Here, the linen has been pre-mordanted with a mixture of alum and iron(II) sulphate aka green vitriol, aka ferrous sulphate. The presence of the iron salt converts the orange-coloured tannin extract to a medieval ink, as discussed by Dr.J.Accetta in his St.Louis presentation of October 2014

Here's a 3D rendering in ImageJ of the alum-premordanted image.

I hope these imprints convey the potential of dye-imprinting for modelling at least some of the features of the Shroud image, even if, for now, one has to be content with some models showing some features, while one continues to search for the Universal Model that displays all of them simultaneously The immediate difficulty re the terracotta template was that some of the clay transfers as well as dye - one can see patchy areas of red-brown in the above image that are distinct from the greenish-brown of the dye-mordant combination. I had tried to minimize clay transfer (spotted in preliminary experiments) by oven-baking followed by varnishing with gum arabic (the latter being cited as a likely ingredient in Accetta's paper as a viscosity-raising agent, which I employed primarily for its quick-drying varnish-like properties).

Reluctantly, I decided to return to the brass crucifix as template for some further experimentation.

The fainter of the two imprints on the left was from untreated tannin extract from pomegranate and uncoated template. The better imprint on the right was from the template after varnishing with gum arabic.

However, the problem with gum arabic is its colour: the solution  has to be a dark brown before there's a noticeable increase in viscosity, i.e. 'thickness'.  The last thing one wants when experimenting with an orange or yellow dye is colour from other sources - whether clay particles or varnish. So the gum arabic was dispensed with in these final imprintings from the crucifix.

Spot the crystal of alum that has been added to the tannin extract. The latter, initially orange, turns a brownish-green, and can then be used in so-called 'meta-mordant' mode. That's when dye and mordant are introduced simutaneously, a procedure that is less kind on the cloth if both dye and mordant are acidic.(See wiki entry on mordants).

Alum meta-mordanted imprint of tannin extract. Linen being peeled back from template in the LOTTO configuration.

A pinch of iron (II) sulphate has been added to the tannin extract, and immediately one sees conversion to a dark ink, an approximation to Accetta's "iron gall" ink that goes back to the medieval period based on oak galls (I have substituted pomegranate).

That's the iron/tannin imprint off the crucifix. One can see the bag on the left with the "green vitriol" that converted the tannin dye to medieval ink.

There are tests to be done on colour-fastness - to see if alum and/or iron improve the permanence of the imprint, notably with laundering (though it's a moot point as to whether  the Shroud has ever been wet-laundered or not). One then moves onto the difficult phase, namely to see whether the imprints one sees above might ever be capable of generating a fainter more subtle  'ghost' imprint that more closely matches the properties of the Shroud, especially those reported to exist at the microscopic level (extreme superficiality, conjectured confinement to the primary cell wall of retted flax fibres,  half-tone effect, striation, discontinuous colour distribution etc). See the posting that immediately precedes this one for more details on the hypothesized Mark 2 'ghost imprint'.

However, there's a practical matter that needs to be addressed. Although it was possible in these experiments to obtain a very satisfactory imprint with thedissolved  tannin extracts, almost indistinguishable in sharpness from scorch imprints, there was the inevitable bleed-though to the reverse side to a greater or lesser degree. Thicker linen helped reduce that effect, just as thicker grades of linen help to reduce reverse-side scorching, the latter having been wrongly claimed to be an 'insuperable' objection to thermal imprinting, at least with sensible precautions re temperature control and time of contact. Joseph Accetta recognized the problem of reverse-side colour, suggesting that viscosity-increasing agents could have been used in the dye or ink extracts, gum arabic especially. 

Having obtained front-side imprints without needing gum arabic (except for the imprinting off the terracotta template where the gum was deployed primarily as a sealant and/or undercoat - not wholly effective) I shall now do some more imprints with gum arabicdispersed in the dye or ink and see if there is indeed less reverse-side bleed-through.

 Tuesday March 31st

So what about mixing the tannin extract first with a thickening agent, like the gum arabic suggested by Accetta? Does that help to 'validate' wet dye or ink imprinting by confining the imprint to the one side of the linen?

Gum arabic comes in the form of large brown crystals, rather like the mega-crystals that are sometimes served up with coffee. They go gooey when one adds water, and it takes time and much stirring to get a strong solution. even when dark brown, the latter did not seem particularly viscous (an ominous sign).

Here you see gum arabic solotion (in the small beaker) being added to pomegranate extract.  (My pictures are no longer accepting captions for some reason).

The crucifix has been painted with the tannin/gum mixture, linen laid on top, and the latter firmly pressed down to capture relief. Here's the appearance, which thus far looks promising (no bleed-through being apparent).

Here's the very satisfactory imprint one sees on the contact side when the linen is pulled back.

Oh dear. This is the reverse side, photographed straight afterwards, and already one can see bleed-through, despite the presence of that thickening agent. Late addition: the gum arabic was then left to evaporate in air until a treacly consistency, that was then painted onto the crucifix. despite the higher viscosity than used with dye, there was immediate bleed-through to the reverse-side of the linen.

(See postscript at end for an aside on the unusual properties of gum arabic syrup).

Gum arabic is, sad to say,  NOT the answer if one's attempting to achieve contact-side imprinting only. Maybe there are alternatives that need testing, but they have to fulfil a number of criteria yet to be discussed in detail.

Maybe one needs to test a starch dispersion, or collagen glue from boiling animal bones etc? Suppose it imprinted well, with minimal bleed through. Suppose it was then prone to flaking off with ageing and/or handling, leaving that fainter ghost image which is what we may be seeing today. There's still work to be done. But first I must report the results of testing out a different scenario by which a ghost image could have formed, one that results in a modification of superficial linen carbohydrates, based on the premise that alum and/or iron sulphates used as mordants or ink ingredients could have generated sulphuric acid that at sufficiently high local concentration MIGHT react chemically to produce changes not dissimilar to those obtained by thermal means (contact scorching). For that, the experiments moved from kitchen to garage, involving as they did a degree of hazard. 

Here's a hint (above) of what to expect.

Time now to start another posting - reporting on what  battery acid (sulphuric acid of intermediate concentration) does - and does not do-  to linen as it slowly evaporates to become more concentrated.

Postscript on gum arabic (after standing in air to become a saturated soution, or nearly so).

The gum arabic syrup was added in a series of drips to this polythene surface. It's quite viscous, as seen when one tilts the plastic - it slowly creeps downwards.

After a few hours exposed to the air, the drips have solidified. But they do not stick to the polythene. Flexing the plastic, or touching the solidified material with the end of a pencil is enough to make them detach and fall to the bottom.

Here they all are, detached and bunched up together. Even the air bubbles have been 'captured' on solidifying.

The material you see above is highly brittle. It needs only the back of a a teaspoon to break it up into sharp fragments.

Conclusion? The treacly gum arabic solution that was able quickly to penetrate the weave of the linen to the opposite side must have been close to saturation, given the rapidity with which it changed into a solid.

Afterthought: despite the capillary migration of treacly gum arabic, is it neverthess a possibility that it was the SOLE imprinting agent, with no dyes, no mordants, nothing in fact except gum arabic? How couid that be, one might reasonably ask? Answer: because an image imprinted with wet gum arabic quickly sets to leave a shiny solid, rigid varnish-like 'shell'  on the cloth. The solidified gum is brittle, as seen above, so it's then possible to knead the linen so as to break it up, leaving a much fainter image. While not at the top of my list of priorities, it's a minimalist 'solution' to the TS enigma that needs looking at, if only to exclude it for failing to meet this or that criterion.