Look carefully at the sepia photograph on the left. There are two important things you need to know about it. Firstly, while it is a photographic positive, it might reasonably be described as a pseudo-negative. Why? Because of the position of the studio light, illuminating the subject from below and slightly to one side so that a feature like the nose, say, that normally appears light in a photograph is plunged into shade created by the subject’s chin etc, and now appears dark.
Now look at the picture on the right. It is a light/dark reversed negative, but because the original was a pseudo-negative, it in fact looks more like a positive.
Ring any bells? Yes, the sepia image of the Man in the Turin Shroud has often been described as a pseudo-negative, ever since Secondo Pia in 1898 discovered the near-miraculous transformation achieved by converting to a real negative, and finding it too looks more like a positive (no doubt for the same reasons).
Some have seized on photographic terminology and jumped to a false conclusion –namely that the Shroud image is itself a photograph, suggesting there was a miraculous burst of energy in a 1st century tomb that somehow imprinted the image of a shroud-enclosed corpse onto the linen. Quite how that was achieved without a light-receptive ‘photographic’ emulsion, or converging lens, chemical developers or the other paraphernalia of the photographic studio we are not told, and in any case that narrative does not square with the carbon dating (1260 to 1390). Another theory says that the Shroud image was made by Leonardo Da Vinci ( 1452-1519 ), perhaps using a camera obscura, but Renaissance Man came along too late to fit the C-dating.
In any case, it is the job of scientists like myself (albeit long retired) to develop testable ideas and theories that fit with the available evidence, and which do not require paranormal explanations much beloved of today’s enigmati. (Goodness knows what they are putting in the pizzas these days).
To show I mean business, I will now tell you something else about that image above that I have so far withheld, something that may have contributed to the subjective enhancement achieved by converting the Shroud-like pseudo-negative to a real negative (and thus a pseudo-positive).
Some of you may have guessed already. The image is more Shroud-like than you may have imagined. It is that of Frederik Chopin ( 1810-1849). What’s more, the one on the left is his death mask. So if you were thinking it had a somewhat sepulchral quality to it, you were right. But can the same be said of the pseudo-positive? It’s a matter for individual judgement, obviously, beauty, especially post-mortem beauty being in the eye of the beholder, but had I been shown the image on the right, I for one would not have immediately declared it to be that of a corpse. Asleep perhaps, possibly unconscious, or maybe just deep in thought, mentally composing one of his Nocturnes?
One thing leads to another. I long ago suggested that the image of the Man in the Shroud was obtained by thermal imprinting (“scorching”) from a template, fashioned perhaps in heat-resistant metal or ceramics. I refined the idea by suggesting that the template was thrust into linen spread over a bed of sand or similar to get a good imprint, and that the template (uncharitably described by some wag as a “tin man”) was either a full 3D statue , say a bronze, or maybe two separate front and back shallow bas-reliefs.
Well, you can probably guess what is coming, based on that image above, and the way that the pseudo-negative responds Shroud-like to being light/dark reversed. I now propose that the Shroud image was produced by medieval artisans who began with the body of a dead man, from which they obtained a death mask from the face, and then from the rest of the body, either in one go, or in separate sections later married up.
To get the death mask, the face was first smeared with oil, the hair especially, and then coated with plaster of Paris or something similar that sets solid. The mask was then carefully detached from the face (and body) and used as a mould for producing a bas-relief replica, e.g. by coating the inside with oil, and then filling with more wet plaster.
On setting, the “positive” replica was removed from the mould, and then heated and pressed into linen to produce a faint and superficial scorch – the latter being a negative image of the original subject. But the scorch was NOT a photographic image, note, but a thermal imprint, so it’s perhaps better to call it a pseudo-negative. If it is to be described as some kind of x–graph, then it is a thermograph, or maybe a pyrograph (see Irene Corgiat’s use of an electric pyrotool – rather like a hot soldering iron – to produce a passable imitation of the man in the Shroud)..
SUDDEN THOUGHT: Maybe those prominent lines above the head and below the chin are NOT scorched-in crease marks as I have proposed earlier: Why does the Turin Shroud appear to have scorched-in crease marks? Tell-tale signature for medieval forging?
Maybe the plaster template cracked in at least two places when being thrust into the linen, creating a small gap!
I believe this theory can explain a number of subtleties regarding the Shroud image. But for now, the point I would stress is that it accounts for the startling transformation that can be achieved in a single photographic step – converting an unattractive (and some might say somewhat grotesque) pseudo-negative into a more life-like image – and a serene and luminous one at that.
Even photographs that are not any kind of negative, pseudo- or otherwise, can benefit from being turned into real photographic negatives, contrary perhaps to one’s expectations. See some examples below.
In conclusion,the remarkable transformation of the Shroud image achieved first by Secondo Pia in 1898 is due to the coupled linking of three entirely artisan-like activities: first the production of a 3D replica of a real human being, albeit deceased, i.e. a death mask, secondly the production of a thermal imprint from the replica that was a pseudo-negative, and then finally the conversion of the pseudo-negative back to a positive image with photography. The latter, not surprisingly, contains encoded 3D information, revealed when image density is plotted as relief. See my blog banner at the top of this and other postings, showing an experiment – my own – with a simple metal template that was used to make a pseudo-negative scorch mark. The latter could be converted back to a positive, using simple light/dark reversal, and then displayed as a semi-3D image using ImageJ software to resemble closely the original trinket, with some of the gentle, soft-focus but highly luminous quality of the iconic Shroud image after similar processing (top left of banner).
I’d say we were getting there, wouldn’t you? Think death mask. Think thermal imprinting. Forget about corona discharges, forget about uv laser beams (some of you who may be reading this need to change your pizza supplier).
Colin Berry, retired science bod, August 26th, 2012
Further reading: here’s one I made earlier (March 16th):
How the Shroud’s mask-like face is explained away as irregularities in the linen – a prime example of misinformation and/or clutching at straws
Word of warning to would-be experimentalists, who might be toying with the idea of making a “life mask” as substitute for a death mask :
“The chemical reaction that occurs when plaster is mixed with water is exothermic in nature and can therefore cause severe burns. The potential dangers were demonstrated in January 2007, when a sixteen-year-old girl suffered third-degree burns after encasing her hands in a bucket of plaster as part of a school art project in Lincolnshire, England.
The burns were so severe that she subsequently had both thumbs and six of her fingers amputated. For this reason only thin layers of plaster should be used, with time to cool between layers, or strips of cloth in plaster laid-up in the method used by the medical field. In place of plaster, alginate can safely be used for casting body parts.”