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|
(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.|
|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'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.
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.