I don't think it's a hoax, but at the same time I don't think it's what its supporters claim it to be. For some time now I've toyed with the idea that ionizing radiation might have produced the image. But where would the radiation have come from? If the prototype for the image had been a piece of statuary, it might have come from radioactive elements that occur naturally in many kinds of rocks, especially of the sedimentary variety. Now, the Byzantine story of the Mandylion (which many believe to have been the shroud, folded over and kept within a frame) says that the cloth-bearing image was found in proximity to a "tile" that had an exact copy of the image imprinted on it. Supposedly the cloth had been placed in a niche in the walls of Edessa, and the tile placed in front of it for protection; the image then sat in the niche for several hundred years before its discovery during a siege. Suppose, however, that this story has it backward: suppose that it was the tile that had been placed in the niche, and the cloth placed over it for covering. Over the course of several centuries, radioactive material in the stone might have produced sufficient ionizing radiation to oxidize and discolor the threads of the cloth in proportion to its proximity to the tile, thus producing the image we know as the Shroud of Turin.
The Edessans who discovered the tile would have been hard-pressed to explain what they had found, but to their minds the image on the tile would have appeared less miraculous than that on the cloth. Hence the cloth would have been regarded as divinely wrought.
You may have a good idea. Radiologists who have looked at the Shroud state that not only is it a negative photograph, it is also an X-RAY. To the trained eye of a radiologist the bones of the hands, forearms, teeth and skull are visible under the skin and muscle!
From
NUCLEAR MEDICINE AND ITS RELEVANCE TO THE SHROUD OF TURIN (PDF file, requires Adobe Acrobat Reader)
by August D. Accetta MD, Kenneth Lyons MD, John Jackson PhD.
"The Shroud image suggests quite strongly the presence of many skeletal details e.g. carpal and metacarpal bones, some 22 teeth, eye sockets, left femur, left and possibly right thumbs flexed under the palms of the hands, as well as soft tissue and soft tissue injuries; all presumably originating from some form of radiation emitted from the body enshrouded.
Testing done on a human volunteer (a radiologist) injected with a radioactive tracer (technicium99m) and then scanned with a collimated gamma camera exhibited the greatest likeness to the image on the shroud (minus the blood stains) of all attempts to re-create a shroudlike image. The sole exception to this was the head... the scan of the volunteers head turned out to be a caricature with no detail at all.
As I understand it, Scans (which can take up to 30 minutes each) are done at various times after injection of the tracer because the radioactive tracer infuses different parts of the body at different rates. First to be infused are the active, blood filled parts of the body, then more dense structures, and finally, the bones. The image is then constructed from these timed scans by a computer "sophisticated" computer. The head image on the test scans were washed out from too much radiation over too long a period for the scanner.
I had such a radiogram done of my heart on Monday... they did two scans seperated by about an hour... they did not need to see the bones but wanted the tissues of my heart. The "sophisticated computer" used to generate the image from the scanner they used on me was a 14 year old Macintosh IIFX!
Although not detailled in the paper, Dr. Arcetta told me at a Shroud symposium that the lack on the Shroud of some deeper details seen on the radiograms of the test subject (only structures less than ~3/8 inch deep are seen on the Shroud while the radiogram goes all the way to the core), and the inclusion of details that would have come at different infusion times (soft tissue and hard tissue nearly equally represented), lead to a startling conclusion: the varied tissues of the body covered by the shroud became radioactive at the same time... and that the radiation was some how STOPPED before the radiation deeper in the body reached the surface of the shroud.
This would explain the detailed facial image! But how do you stop the deeper radiation from radiating and exposing the deeper structures? The only answer they could come up with was to either remove the shroud from the body or REMOVE THE BODY FROM THE SHROUD . . . ALMOST INSTANTLY.
How fast does Gamma Radiation travel 3/8 of an inch????
Incidentally, the production of such an image requires a COLLIMATED CAMERA that only accepts radiation in the Z axis... how did this occur in a 1st (or 13th) Century piece of linen? The image on the Shroud is vertically collimated. There is no image of the sides, no distortion that would be caused by gamma radiation from other angles hitting the shroud in the same spot as a gamma particle in the Z axis. The Gamma Cameras cost hundreds of thousands of dollars.