See also my "Medieval photography: Nicholas Allen" post of 7 August 2016.
[Above: How a medieval forger supposedly created the Shroud of Turin, "photographically, in a camera obscura," based on a model by Prof. Nicholas Allen: Wilson, I., "The Blood and the Shroud," 1998, p.214]
in a camera obscura, was the image burnt on by pressing the cloth against a heated sculpture? I responded to "Was it created photographically" in general at the end of part #2. As for "Was it created ... in a camera obscura?" i.e. as proposed by Prof. Nicholas Allen (see above). The short answer is no, because the "camera obscura" was the "ancestor of the photographic camera" (my emphasis):
"camera obscura ... ancestor of the photographic camera. The Latin name means `dark chamber,' and the earliest versions, dating to antiquity, consisted of small darkened rooms with light admitted through a single tiny hole. The result was that an inverted image of the outside scene was cast on the opposite wall, which was usually whitened. For centuries the technique was used for viewing eclipses of the Sun without endangering the eyes and, by the 16th century, as an aid to drawing; the subject was posed outside and the image reflected on a piece of drawing paper for the artist to trace. Portable versions were built, followed by smaller and even pocket models; the interior of the box was painted black and the image reflected by an angled mirror so that it could be viewed right side up. The introduction of a light-sensitive plate by J.-N. Niepce created photography." ("camera obscura," Encyclopaedia Britannica Online. Accessed 12 July 2007)
that is, "The forerunner of the camera" (my emphasis):
"photography, history of Antecedents ... The forerunner of the camera was the camera obscura, a dark chamber or room with a hole (later a lens) in one wall, through which images of objects outside the room were projected on the opposite wall. The principle was probably known to the Chinese and to ancient Greeks such as Aristotle more than 2,000 years ago. Late in the 16th century, the Italian scientist and writer Giambattista della Porta demonstrated and described in detail the use of a camera obscura with a lens. While artists in subsequent centuries commonly used variations on the camera obscura to create images they could trace, the results from these devices depended on the artist's drawing skills, and so scientists continued to search for a method to reproduce images completely mechanically. In 1727 the German professor of anatomy Johann Heinrich Schulze proved that the darkening of silver salts, a phenomenon known since the 16th century and possibly earlier, was caused by light and not heat. He demonstrated the fact by using sunlight to record words on the salts, but he made no attempt to preserve the images permanently. His discovery, in combination with the camera obscura, provided the basic technology necessary for photography. It was not until the early 19th century, however, that photography actually came into being." ("photography, history of: antecedents," Encyclopaedia Britannica Online. Accessed 12 July 2007)
not the photographic camera itself.
As the above Wikipedia entries state, "It was not until the early 19th century" with "The introduction of a light-sensitive plate by J.-N. Niepce" (in 1824, i.e. over 300 years after Leonardo's death) that "photography actually came into being" (my emphasis)!
Now as for Allen's experiment to test his medieval photograph theory, Brendan Whiting summarised it as follows:
"The Camera-Obscura Theory In 1995 a theory that the Shroud image might have been created through the application of an early, crude form of photography known as camera-obscura - supposed to have been utilised in the Middle Ages - was tested by Professor Nicholas Allen, a dean of the Faculty of Art and Design at the Port Elizabeth Technikon in South Africa [Allen, N., "Verification of the nature and causes of the photo-negative images on the Shroud of Lirey-Chambery-Turin," De Arte, April 1995, pp.31-34]. Allen knew that the image on the Shroud was not a painting, and was aware that in medieval Europe, Italy in particular, there existed knowledge of the use of quartz for making lenses for magnification purposes. He was also aware that at that time there was knowledge of silver salts, which had the properties required for converting into light-sensitive chemicals. To test his theory Allen constructed a camera obscura in the form of a room that was totally dark except for an aperture in the front wall, in which he set a type of rock-crystal lens that he believed could have existed in the Middle Ages. He soaked a shroud-like cloth in light-sensitive silver nitrate, folded it in half across the middle, and installed it vertically in the middle of the room, some 5 metres from the aperture, while it was closed. For the subject to be `photographed' he made a plaster cast from a naked and bearded male life-model who had stood in a death-like pose, as similar as possible to that of the man of the Shroud. He suspended the plaster cast vertically in full sunlight, about 5 metres in front of the aperture outside the room, having precalculated that at this distance from the lens the subject's image would be exposed on the light-sensitive cloth life-size and upside-down. He opened the aperture and kept it open for several days, during which the plaster cast remained exposed to sunlight. The result was a `negative' exposure of the front of the cast-image on the cloth. To produce a double image, front and back, he repeated the process, closing the aperture, turning both the plaster cast and the folded cloth around, then opening the aperture for several more days. To complete his experiment he had the cloth washed in a solution of ammonia salts to remove the silver salts, thus `fixing' the exposures. The entire experiment was conducted according to his hypothesis that he had replicated a form of photography believed to have been known in some scientific circles in medieval Europe." (Whiting, B., "The Shroud Story," Harbour Publishing: Strathfield NSW, Australia, 2006, pp.158-160. Emphasis original).
But artist-physicist Isabel Piczek pointed out that, amongst other things: 1) "the camera obscura ... was not a primitive photo camera, but a device used by artists to aid in representing buildings and open space in perspective"; 2) "at the time the [photo]chemical properties of silver nitrate were unknown"; 3) "there was no knowledge of ... the properties of light employing a bi-convex, finely ground quartz lens"; and 4) "a real corpse would have been required, and would have to hang in the sun for fourteen days" but "the image on the Shroud is of a corpse in a state of rigor mortis and ... `corpses do not maintain rigor mortis" for "fourteen days in the sun" (my emphasis):
"The idea that the Shroud is a primitive photograph was further explored by Nicholas Allen, dean of the Faculty of Art and Design at Port Elizabeth Technikon, in Port Elizabeth, South Africa. Allen proposed that the Shroud could have been created in the fourteenth century by an artist who used: (1) rock crystal; (2) silver salts; and (3) salt of ammonia (found in urine), all of which would have been available at the time. In his article entitled `Verification of the Nature and Causes of the Photo-negative Images on the Shroud of Lirey-Chambery-Turin' he argued that the Shroud `could have been' produced by a form of primitive photography. This `hypothetical photographic technique,' Allen insisted `... is the only plausible explanation for the image formation on the Shroud ... and indicates that people in the late thirteenth and fourteenth century were indeed privy to a photographic technology which was previously thought to be unknown.' The South-African scholar constructed a device known as a camera obscura. The size of a typical living room, it was built so that no light could get in except through a small opening for a rock crystal lens. He closed this opening and prepared a cloth made to the same dimensions of the Shroud, and, folding it once across its width and soaking it in light-sensitive silver nitrate, hung it up inside the camera obscura fifteen feet from the lens. When the cloth dried it became a sort of unexposed film. Next he made a plastic cast of a living man of roughly the same size and shape of the man of the Shroud. Allen then suspended the statue in the sunlight fifteen feet in front of the lens. His object was to project the image of the statue through the lens onto the cloth. After several days the reflection of the statue imprinted a negative onto the cloth. Allen then closed his improvised shutter and turned the statue around so that the back faced the lens, which he opened for several more days in order to create a front and back image similar to that of the Shroud. So that the negative would not fade from exposure to light, Allen washed it in a solution of ammonia salts. Although the process devised by Professor Allen produced an image with many characteristics of that of the Shroud of Turin, some have questioned whether it really could have been carried out in the Middle Ages. ... Isabel Piczek rejected Allen's hypothesis. First of all, she argued, the camera obscura that figured prominently in both the theories of Allen and of Picknett and Prince was not a primitive photo camera, but a device used by artists to aid in representing buildings and open space in perspective. Although it was used by the Greeks and the Romans, it was not used in the Middle Ages. While Allen argued that all the materials needed for making a photograph were available by the thirteenth century, Piczek pointed out that at the time the chemical properties of silver nitrate were unknown, and there was no knowledge of optics `or the properties of light employing a bi-convex, finely ground quartz lens.' The medieval photographer would have had to know the properties of ultraviolet radiation `before electromagnetism was known at all' and he would have had to known how to stabilize his image through the use of ammonia. Since it was unlikely that medieval technicians could produce a body cast of the quality Allen devised, a real corpse would have been required, and would have to hang in the sun for fourteen days. Piczek pointed out that the image on the Shroud is of a corpse in a state of rigor mortis and the fact is that `corpses do not maintain rigor mortis [and] cannot hang fourteen days in the sun, or else you would not care to see what the camera obscura would bring in onto your canvas,' [Piczek, I., "Alice in Wonderland and the Shroud of Turin?," Holy Shroud Seminar Retreat at Mount Esopus, New York, August 24, 1996, pp. 8-9] (Ruffin, C.B., "The Shroud of Turin: The Most Up-To-Date Analysis of All the Facts Regarding the Church's Controversial Relic," Our Sunday Visitor: Huntington IN, 1999, pp.140-142)
In fact "it was not until 1556" (i.e. 37 years after Leonardo's death) "that the light sensitive nature of silver nitrate was rediscovered" by Georg Fabricius (1516-1571) and even then "he found this discovery of little interest." It was not until 1725 (i.e. 206 years after Leonardo's death) that "Johann Heinrich Schulze proved that the darkening of silver salts ... was caused by light and not heat":
"Despite the translation of much of Geber's ["the Arab alchemist Jabir Ibn Haiyan ... (ca721-803CE)"] work, it was not until 1556 that the light sensitive nature of silver nitrate was rediscovered. Georg Fabricius (1516-1571) from Chemnitz added salt to silver nitrate solution, forming a white solid, silver chloride, which went black in sunlight. However because of his theoretical ideas he found this discovery of little interest. Fabricus's researches were wide ranging: as well as being an alchemist, he was a poet, teacher, historian and archaeologist, and was probably best known for his popular guide-book to the antiquities of Rome. Fifty years later in 1614, Angelo Sala (1576-1637), an Italian Calvinist who left Italy to avoid religious persecution to settle first in the Low Countries and later Hamburg, published a paper including his work with powdered silver nitrate. He found this turned black on exposure to the sun, although he did not make it clear whether this was due to the light or the heat of the rays. He also found that it stained paper black if in contact with it. .... Robert Boyle (1627-91) also noted the blackening of silver nitrate on exposure in 1667, but he put it down to the action of air on the material. Although one of the most eminent scientists of the time he apparently jumped to an incorrect conclusion without examining the evidence or carrying out suitable experiments. Further work on the light-sensitivity of silver salts was carried out in 1693-1694 by German chemist Wilhelm Homberg (1652-1715). One of his experiments involved dipping bone in silver nitrate solution; it then darkened in sunlight. Homberg showed the darkening was due to the rays of the sun, but, like Sala, failed to make clear whether it was a result of their light or heat. It was not until the work of Johann Heinrich Schulze in 1725 that this was sorted out, (although there were further confusions over the next 75 years.) Schulze noticed the effect (using chalk dipped in silver nitrate and nitric acid) and tried to reproduce it with heat. When these experiment failed he turned to the effect of light, and found that this produced the darkening. Schulze carried out a number of lecture demonstrations using card with cut shapes wrapped around silver nitrate bottles and produced darkening giving a crude impression of these shapes in the solution." ("Photo History - Finding the chemistry, Part 2: Alchemy to Chemistry," About.com)
Indeed, it was not until "about 1795" (i.e. 276 years after Leonardo's death) that "The fantastic possibility of producing images by the action of light ... occurred to anyone as a serious thought" when "Thomas Wedgwood ... narrowly missed becoming the inventor of photography" and so it was not until "1816" that "Joseph Nicephore Niepce ... set out to take pictures from
nature using a camera and paper sensitized with silver chloride" but even then he had only "limited success almost immediately ... because the image tones were ... negative ... and he could not make the image permanent" but "At last, in 1826" (i.e. 297 years after Leonardo's death) "he succeeded" and produced "The world's first permanent camera image" (my emphasis):
"In 1777 Carl Wilhelm Scheele, the Swedish chemist, investigated the properties of silver chloride and made some interesting discoveries. Like Schulze, he established that the blackening effect on his silver salt was due to light, not heat. He also proved that the black material was metallic silver and he noted that ammonia, which was known to dissolve silver chloride, did not affect the blackened silver. If Scheele had realized the importance of this last discovery, he could very well have become the inventor of photography because by this time the essential processes were known. Silver chloride could be reduced to black metallic silver by exposure to light; ammonia could preserve the image by dissolving the silver chloride without harming the image tones; and, of course, the camera was still waiting in the wings. But Scheele's investigations were only noted in passing. The world was not yet ready for photography. The fantastic possibility of producing images by the action of light had simply not occurred to anyone as a serious thought. This essential idea finally came to Thomas Wedgwood, the youngest son of the famous potter, Josiah. In addition to being an outstanding craftsman and artist, Josiah was a brilliant and respected member of the English scientific community. Thomas was familiar with the camera obscura because his father had used it as an aid in drawing scenes for use on his pottery. The Wedgwood family also owned the notebooks of William Lewis, who in 1763 had described Schulze's and his own experiments with the silver compounds. These circumstances and natural curiosity prompted young Thomas to begin experiments of his own, probably about 1795. Thomas Wedgwood narrowly missed becoming the inventor of photography for two reasons. He gave up attempts to make pictures with the camera obscura (his exposures were not sufficient), and he was unable to fix the silver images he did produce by direct printing. In France, meanwhile, Joseph Nicephore Niepce and his son Isidore were busy experimenting with lithography at the family estate near Chalon. ... Nicephore began to explore light sensitive varnishes, hoping to find a coating for the stones that would record the drawings by exposure to light. He must have made some progress because in 1816 he set out to take pictures from nature using a camera and paper sensitized with silver chloride. Niepce had limited success almost immediately, but he was displeased because the image tones were reversed from nature (they were negative) and he could not make the image permanent. He realized that the tonal reversal was an inherent part of the silver process and tried to produce a positive print by reprinting one of his negatives, but his attempts were unsuccessful. He also found that nitric acid helped to preserve the image for a while, but it only postponed disaster and could not prevent it. He began to experiment with other materials. Finally, in 1822 he produced a copy of an engraving by exposing through the original onto a glass plate coated with bitumen of Judea, a type of asphalt. Light hardens this material, so when Niepce washed his exposed plate with the usual solvents, only the unexposed portions were floated away, leaving the image in permanent lines. He called his process heliography (sun writing). He made a number of similar heliographs in the next few years and continued his efforts to record a camera image. At last, in 1826, he succeeded. The world's first permanent camera image shows the view from Niepce's second floor window and is little more than an impression. It is a bitumen image on pewter, showing only masses of light and dark tones. The exposure supposedly took about eight hours." (Hammerstingl, W., "The beginnings of Photography," 1999)
So all photographic theories of explaining the Shroud's existence in the 14th century (or even the 15th century) fail by being hopelessly anachronistic in requiring that someone (e.g. Leonardo) in the Middle Ages invented the whole process of photography, from: 1) discovering that silver nitrate was light-sensitive; 2) discovering how to fix silver nitrate images; 3) taking the 4.3 x 1.1 metre photograph of a man (or model) crucified exactly as Jesus was (arguably the greatest photograph ever taken!); 4) recording that image on linen covered with silver nitrate; but not 5) knowing how to convert the negative image to a positive; and then 6) not doing any other photographs; nor 7) telling anyone else; or 8) writing down for posterity his great discovery!
Not to mention the `minor' matter that the Shroud of Turin is a colour, namely sepia, whereas Allen's image obtained from silver nitrate is necessarily black and white!
[Above: Black and white Shroud `replica' produced by Prof. Nicholas Allen (Wilson, I., "The Blood and the Shroud," 1998, plate 47c) compared with actual sepia coloured Shroud (Examine The Shroud of Turin)]
And as Wilson pointed out, even if "someone of the Middle Ages having successfully mastered such an advanced degree of photographic expertise ... this would have been directed solely to producing a `negative' image that to any mediaeval observer could only have seemed most unconvincing" since the "`positive' photograph would still have been inaccessible to ... even the `photographer' who created it, for another five hundred years" (my emphasis):
"Furthermore, it cannot be stressed enough that even in the unlikely event of someone of the Middle Ages having successfully mastered such an advanced degree of photographic expertise - only then to lose it again this would have been directed solely to producing a `negative' image that to any mediaeval observer could only have seemed most unconvincing. The so compelling hidden `positive' photograph would still have been inaccessible to anyone, even the `photographer' who created it, for another five hundred years." (Wilson, 1998, p.217).
The final nail in the coffin of Allen's medieval camera obscura photograph theory (and indeed to all such medieval photograph theories) is that it requires the artist/photographer to "produce subtle photographic details, like scourge wounds and bloodstains, all from a total distance of 10 metres." Allen tried to get around this by claiming that, "The stigmata and other areas of the blood of the Shroud were probably added with the aid of a paintbrush and real blood, after the negative image had been obtained" but in fact "there are no signs of any body image beneath the bloodstains, meaning that the blood wounds penetrated the fibres before the image appeared on the cloth" (my emphasis):
"The result was images which bore a number of similarities to the Shroud image when viewed by the naked eye. The cloth had developed a straw-yellow discoloration of its surface fibrils, and faint evidence of an image of the plaster-cast was apparent when the cloth was viewed from about 2 metres distance. The most telling effect became evident when he photographed his cloth with a modern camera, using black-and-white film, and examined the negative. It revealed a `positive' image of the subject. While his experiment might have supported his conclusion, `that people in the late thirteenth or early fourteenth century were privy to a photographic technology which was previously thought to be unknown before the beginning of the nineteenth century' [Allen, Ibid., p.34], it would be an extreme interpretation of his work for him or anyone to claim that the Shroud images could have been created in a similar way. Not only would it have required the procurement of a Jewish male corpse, crucified in the same way as Jesus, with the nail and lance wounds, and for it to be suspended for several days in sunshine, facing the aperture, then for several days more with its back facing the aperture, without displaying any sign of decay, and also produce subtle photographic details, like scourge wounds and bloodstains, all from a total distance of 10 metres. To have fulfilled such onerous requirements is beyond belief. Yet, in attempting to dispel disbelief that the Shroud image could have been formed in this way Allen wrote: `The stigmata and other areas of the blood of the Shroud were probably added with the aid of a paintbrush and real blood, after the negative image had been obtained'. This was not possible, for the simple reason that scientists have discovered there are no signs of any body image beneath the bloodstains, meaning that the blood wounds penetrated the fibres before the image appeared on the cloth. With all photography the choice of film and the purity of the developing emulsions define the degree of sharpness and clarity of a photographic image. The fact that no museum or library in the world possesses a medieval camera-obscura photograph or even a crude pre-1800 photograph is sufficient evidence that no one had produced one before the invention of photography." (Whiting, 2006, pp.160-161).
Therefore, as Ian Wilson pointed out, because "to date there has been only one genuinely satisfying, albeit still only partial, replication of the Shroud's image, that by Professor Nicholas Allen" but that demands so much ingenuity and advanced photographic knowledge on the part of someone of the Middle Ages that it may actually" (and in fact does) "represent rather better evidence for the Shroud's authenticity than for its forgery" (my emphasis)!:
"As for the fundamental questions for anyone adopting the forgery hypothesis - for example: `Who forged such an extraordinary image?' 'How did he do so without betraying any obvious sign of his artifice?' 'How did he manage to get so much right medically, historically and culturally?' - if you ask yourself whether Sox, or any of the other current detractors, from McCrone and Hall to Picknett and Prince, has yet offered any genuinely satisfying answers, the response has to be no. Indeed, if anyone had come up with a convincing solution as to how and by whom the Shroud was forged, they would inevitably have created a consensus around which everyone sceptical on the matter would rally. Yet so far this has not even begun to happen. Realistically, to date there has been only one genuinely satisfying, albeit still only partial, replication of the Shroud's image, that by Professor Nicholas Allen. And that demands so much ingenuity and advanced photographic knowledge on the part of someone of the Middle Ages that it may actually represent rather better evidence for the Shroud's authenticity than for its forgery." (Wilson, I., "The Blood and the Shroud: New Evidence that the World's Most Sacred Relic is Real," Simon & Schuster: New York NY, 1998, p.235).
To be continued in part #4 with my response to: "Was ... the image burnt on by pressing the cloth against a heated sculpture?"
Posted: 13 July 2007. Updated: 26 August 2016.
"The figures on the Shroud, in fact, are not paintings at all. As already stated, they are negative images; and the idea of a negative became known only through the invention of photography in the 19th Century. No artist of any earlier period, therefore, (certainly none of the 14th Century and, above all, none before the 5th), could have conceived the idea of painting a negative. The figures, moreover, are very exact negatives. When they are photographed, they appear on the film with the natural proportions of a full-grown man, with a true perspective, with a noble, impressive countenance, and with a minute fidelity to nature even in minor details. Each one of these points involves principles of science and of art which were unknown or poorly grasped until comparatively modern times. It is hard enough to carry out these principles in an ordinary positive painting, in which the lights and shades have their normal values. On the Shroud, they are perfectly illustrated with the lights and shades reversed, though it takes a photograph to reveal the fact. Even today no artist can paint so exact a negative. No artist, in fact, has yet succeeded in making an exact copy of the negative figures on the Shroud, though competent artists have made the attempt." (Vignon, P., "The problem of the Holy Shroud," Scientific American, Vol. 156, 1937, pp.162-164, p.162)