I haven't read The Da Vinci Code but...

. . . I have scanned a book by the painter David Hockney, whose internet-driven survey of Renaissance and post-Renaissance art makes a strong case for a trade secret: use of a camera obscura technique for creating precision realism in paintings.

Hockney's book, Secret Knowledge: rediscovering the lost legacy of the old masters, 2001, uses numerous paintings to show that European art guilds possessed this technical ability, which was a closely guarded and prized secret. Eventually the technique, along with the related magic lantern projector, evolved into photography. It's possible the technique also included the use of lenses and mirrors, a topic familiar to Leonardo da Vinci.

Apparently the first European mention of a camera obscura is in Codex Atlanticus.

I didn't know about this when first mulling over the Shroud of Turin controversy and so was quite perplexed as to how such an image could have been formed in the 14th century, when the shroud's existence was first reported. I was mistrustful of the carbon dating, realizing that the Kremlin had a strong motive for deploying its agents to discredit the purported relic.
(See my old page Science, superstition and the Shroud of Turin http://www.angelfire.com/az3/nuzone/shroud.html)

But Hockney's book helps to bolster a theory by fellow Brits Lynn Picknell and Clive Prince that the shroud was faked by none other than Leonardo, a scientist, "magician" and intriguer. Their book The Turin Shroud was a major source of inspiration for The Da Vinci Code, it has been reported.

The two are not professional scientists but, in the time-honored tradition of English amateurs, did an interesting sleuthing job.

As they point out, the frontal head image is way out of proportion with the image of the scourged and crucified body. They suggest the face is quite reminiscent of a self-portrait by Leonardo. Yet, two Catholic scientists at the Jet Propulsion Lab who used a computer method in the 1980s to analyze the image had supposedly demonstrated that it was "three-dimensional." But a much more recent analysis, commissioned by Picknell and Prince, found that the "three-dimensionalism" did not hold up. From what I can tell, the Jet Propulsion pair proved that the image was not made by conventional brushwork but that further analysis indicates some type of projection.

Picknell and Prince suggest that Leonardo used projected images of a face and of a body -- perhaps a cadaver that had been inflicted with various crucifixion wounds -- to create a death mask type of impression. But the image collation was imperfect, leaving the head size wrong and the body that of, by Mideast standards, a giant. This is interesting, in that Hockney discovered that the camera obscura art often failed at proportion and depth of field between spliced images, just as when a collage piece is pasted onto a background.

Still the shroud's official history begins in 1358, about a hundred years prior to the presumed Da Vinci hoax. It seems plausible that either some shroud-like relic had passed to a powerful family and that its condition was poor, either because of its age or because it wasn't that convincing upon close inspection. The family then secretly enlisted Leonardo, the theory goes, in order to obtain a really top-notch relic. Remember, relics were big business in those days, being used to generate revenues and political leverage.

For if Leonardo was the forger, we must account for the fact that the highly distinctive "Vignon marks" on the shroud face have been found in Byzantine art dating to the 7th century. I can't help but wonder whether Leonardo only had the Mandylion (the face) to work with, and added the body as a bonus (I've tried scanning the internet for reports of exact descriptions of the shroud prior to da Vinci's time but haven't succeeded).

The Mandylion refers to an image not made by hands. This "image of Edessa" must have been very impressive, considering the esteem in which it was held by Byzantium. Byzantium also was rife with relics and with secret arts -- which included what we'd call technology along with mumbo-jumbo. The Byzantine tradition of iconography may have stemmed from display of the Mandylion.

Ian Wilson, a credentialed historian who seems to favor shroud authenticity, made a good case for the Mandylion having been passed to the Knights Templar -- perhaps when the crusaders sacked Constantinople in 1204. The shroud then showed up in the hands of a descendant of one of the Templars after the order was ruthlessly suppressed. His idea was that the shroud and the Mandylion were the same, but that in the earlier centuries it had been kept folded in four, like a map, with the head on top and had always been displayed that way.

The other possibility is that a convincing relic of only the head was held by the Templars. A discovery at Templecombe, England, in 1951 showed that regional Templar centers kept paintings of a bearded Jesus face, which may well have been copies of a relic that Templar enemies tried to find but couldn't. The Templars had been accused of worshiping a bearded idol.

Well, what made the Mandylion so convincing? A possibility: when the Templars obtained the relic they also obtained a secret book of magical arts that told how to form such an image. This of course implies that Leonardo discovered the technique when examining this manuscript, which may have contained diagrams. Or, it implies that the image was not counterfeited by Leonardo but was a much, much older counterfeit.

Obviously all this is pure speculation. But one cannot deny that the shroud images have a photographic quality but are out of kilter with each other and that the secret of camera obscura projection in Western art seems to stem from Leonardo's studios.

The other point is that the 1988 carbon analysis dated the shroud to the century before Leonardo. If one discounts possible political control of the result, then one is left to wonder how such a relic could have been so skillfully wrought in that era. Leonardo was one of those once-in-a-thousand-year geniuses who had the requisite combination of skills, talents, knowledge and impiety to pull off such a stunt.

Of course, the radiocarbon dating might easily have been off by a hundred years (but, if fairly done, is not likely to have been off by 1300 years).

All in all, I can't be sure exactly what happened, but I am strongly inclined to agree that the shroud was counterfeited by Leonardo based on a previous relic. The previous relic must have been at least "pretty good" or why all the fuss in previous centuries? But, it is hard not to suspect Leonardo's masterful hand in the Shroud of Turin.

Of course, the thing about the shroud is that there is always more to it. More mystery. I know perfectly well that, no matter how good the scientific and historical analysis, trying to nail down a proof one way or the other is a wil o' the wisp.