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.