What these long-awaited close-up pictures show is the subtlety of the Shroud image fibres, inasmuch as they are a faint yellow, mainly on the most superficial parts of the weave, but with some encroachment into the interstices via the oblique “diving down” threads.
I had previously thought this subtlety was difficult to explain in a simple contact scorch scenario, i.e. by pressing a hot metal template vertically into linen that is spread over a layer of sand or similar. I now realize that was the wrong model, because it did not permit close-enough imprinting, if relying purely on contact between substrate and linen under applied pressure (too much “tenting”). Something more “tactile ” was needed, and if using a hot metal template, a means of detecting heat (and minimizing over-scorching) by finger-tips alone.
I now believe I know how it was done, to produce a very faint image, with pale yellow fibres, as per these welcome pictures, mainly but not exclusively on the more superficial crowns.
Basically what it required was a reversal of the geometry I had been using previously, now laying a hot metal template down onto a hard surface. placing COTTON fabric on top initially, then covering with a double layer of damp cloth, and pressing/moulding around the contours of the template with one’s finger tips. As soon as there is excessive heat detected, one has two options. One is to fold the damp cloth to get a double thickness, and go on moulding to take more heat out of the template until satisfied it will not excessively scorch more expensive linen (though fortunately linen is actually harder to scorch than cotton). When the hot template has passed the finger tip test one takes away the cotton, replaces with linen and repeats the procedure, moulding fabric to contours with finger tips, monitoring temperature. One can lift a corner if need be to check on progress.
Finally, one draws back the linen, and if the result is like the ones I obtained this morning ones sees a VERY FAINT image of one’s template with no reverse side penetration or scorching. It’s in fact difficult to see the image except at a distance (ring any bells?) and under a x10 hand lens there is no obvious localisation of discoloration to the crown threads as might be expected from scorching off an over-hot template. There are subtleties, which I shan’t try to explain now, but ones that might well impact on 3D imaging, giving an odd quality.
The take- away message is this: don’t get too hung up on the science (and I’m as guilty of that as anyone). Think technology – of doing things in slightly different ways to achieve slightly different more subtle end-results, while all the time imagining oneself to be a medieval artisan or similar..
I’ll try and put together a posting in the next day or two of the new results. Warning: one or two oft-cited mantras might be hurt in the making of that post.
I’ll give step-by-step details shortly showing, in a series of snapshots, how the image was produced from the template, to obtain as light or dark an image as desired, and without burning one’s fingers. Needless to say it ain’t rocket science. It’s the kind of technology that a medieval craftsman might anc could have employed to get an image off a template onto (expensive) linen first time. possibly using cheaper cotton for a pilot experiment.
Second instalment: So how was it done (a step-by-step guide)?
Heat brass template (the same crucifix used in previous post) over electric ring. Place down on fabric (linen in these pictures).
Fold fabric to cover template.
Cover with damp floorcloth. Mould the fabric to contours of template, while monitoring heat through layers (stop moulding when it becomes uncomfortable)
Peel back top layer
End result – a faint negative thermal imprint
/contact scorch, ready for uploading to ImageJ for light/dark inversion and 3D enhancement
After image enhancement
Advantages v possible drawbacks of the reversed geometry
Previously I had placed linen (or cotton) on top of damp floor cloth as underlay, then placed template on top of linen and then pressed down on template with something heavy out of the toolbox. That “linen underneath” procedure seemed initially the optimal means of ensuring reasonable imprinting off the contours of the template, especially if bas relief, i.e. shallow relief, without any risk of distortion of image through an excess of wrap-around effect. But there was a heavy price to pay in terms of manageability. One could not easily monitor the degree of scorching under the template, and there was no manual control of moulding of fabric to contours. While guaranteeing a fairly standard result if the temperature was right (checked carefully with small fragments of linen) it deprived the operative(s) of a hands- on experience, and the flexibility that comes with it.
The chief advantage of the reversed geometry, i.e. linen and then damp overlay, is that the fabric can be moulded manually to the template, ensuring that important feautures are not poorly imprinted for lack of contact. Distortion effect? Certainly there is greater risk, but it is not as great as feared, That is because a relatively large thick overlay (a damp floor cloth) has little tendency to wrap around the sides of a 3D template, such that the latter tends to behave in practice as if it were a bas relief, due to imprinting of the highest topmost relief only. Then there is the unexpected bonus of the linen- on- top procedure : provided the overlay is thick and damp, the moulding can be done with bare hands and the degree of heat transfer judged by the rising temperature of the fabric, by appearance of steam when one lifts a corner of the cloth, and even by inspecting the progress of scorching by carefully lifting a corner,
Next instalment: how real is the risk of obverse-side scorching – and the claims that it cannot be avoided and so must invalidate the entire approach?