So sorry, but my dad studies the Shroud as a hobby. Prepare to lose!
(He has conceded that it is most likely man-made. But he is not satisfied with any of the current theories of how it was done. He's not even willing to concede it as a hoax, per se; it may have been made by accident or as an attempt at art.)
Umbran said:
The biggest I can think of being that this process would not produce what looks like a normal photo-negative image.
You are correct that the shroud looks akin to a photo negative image. But any time you wrap the shroud around something (flesh, bronze, whatever) to produce the image, you get the same distortion of the face I mentioend before. So, in order to get what looks like an undistorted photo negative, you'd have to have a very cleverly made statue, distorded so as to produce a normal looking image after the folding. And that's getting into the level of absurdity.
Which is along the lines of what I said: the leading theory has flaws to it.

In order to get the image to look the way it does, the shroud really would have had to be held flat both above and below -- so it would look like a letter U from the side. Possible, but not likely. As for why a statue would produce a negative scorched image: I can't explain that, but the explenation was pretty believable to me. It was in a book that I don't own, however, and I'm already doing two other Google searches right now, so I'm not gonna do another one.
And, as I said, the theory, while better than the others, doesn't seem correct to me.
Umbran said:
Note that the fact that the shroud doesn't have paint on it does not mean that whatever was used to create the image was not painted on. One can imagine, for example, a dye or oxidant could have been painted onto the cloth to produce the image. And an oxidant has, chemically, roughly the same effect as burning by hot bronze.
Just barely possible, but not plausible. There is no paint residue on the Shroud -- at least if those who studied it did their job right; given that multiple groups have done so, I'd say that it is unlikely that *all* of them missed paint residue. To oxidize the cloth, the paint would have had to have been there for some time. It seems unlikely you could get all the paint off, leave the oxidation, and not damage the cloth, all at the same time.
And that doesn't explain why someone would paint a negative image, anyway. No, while I would venture that the Shroud is a work of man, it is a much more clever work than people give it credit for.
Note that this could all work well for a Cthulhu-stylez game: it is assumed to be fake at first, but then explanation after explanation fails. Until the mad cultists get ahold of it and PROVE it isn't man-made...
Umbran said:
One of the leading contenders as the artist in question is Mr. Leonardo Da Vinci himself. I think we're likely to lose if we place bets upon what he woule "never" have done. That's part of genius.
And, any time you bring up Leonardo Da Vinci, you bring up some lovely plot ideas
Okay, so I'm resorting to Google: "Leonardo di Vinci" and "died". I don't even have to follow a link: he died in 1519. The Shroud dates back to *at least* the 1300s. Thus, that theory has about as much veracity as the movie "Hudson Hawk". (Which you should see! Despite its reputation, it is one of the best bizarre comedies I've ever seen.) Not that you couldn't work that into a campaign, though. There are any number of ways you could work di Vinci in with the Shroud; just make it a much younger item than it is. Or maybe he was asked to craft a fake, so that the real image could be locked in a vault to keep it away from the Cthulhu cultists...
Too bad I'm not gonna run any games that could use this any time soon. It has all sorts of possiblities.
