We now KNOW what the image is composed of... and the fine coating of a caramel like substance on the fibers of the image area CAN be created by a Maillard reaction. However, we really don't know that a Maillard reaction was all that was required to created the image. For example, Maillard reactions will occur over time but are usually very slow at normal environmental temperatures. Adding heat, as we do in cooking, will accelerate those reactions. We use this accleration to our benefit, converting sugars into tasty caramels.
Outgassing of such gasses as putrescine and cadaverine would have to follow the laws of gasses which would tend to cause the gasses to dissipate and expand into the atmosphere. The image on the Shroud, however, shows that whatever caused the formation of the image acted in a vertically collimated manner in seeming violation of those gas laws.
It is intriguing that it seemed to have worked only, and equally well, in both vertical vectors, up and down, with absolutely no horizontal vector at all. Gasses don't rise and also fall at the same time at the same temperature, and they certainly don't remain in a column both up and down. Perhaps, putrescine falls and cadaverine rises, or vice verse? I don't know if anyone has done any experiments to determine this.
Perhaps something that radiated from within the body, collimated vertically, and partially shadowed by the internal bony structure, acted as an accelerant to the Maillard reaction only in its direction of action, thereby leaving the imprint of those bones, the metacarpals in the hands and the frontal teeth, in the image. Whatever it was, had to have acted cohesively (almost like a laser) both upward and downward but not with any appreciable amount or angle in any other vector, otherwise the resolution of the image would have suffered and blurred out.
Another problem is that whatever caused the image imprint, effected both living and dead tissue such as the hair and also caused the creation of images of herbs placed around the body (which possibly supported the Shroud over the body, thereby presenting a more flattened receiver).
Whatever it was, had to have acted cohesively (almost like a laser) both upward and downward but not with any appreciable amount or angle in any other vector, otherwise the resolution of the image would have suffered and blurred out.
What is intriguing about this, is that there does not seem to be any *diffusion* of the gases, so that the image remains sharp, with no information being propagated horizontally; secondly, as pointed out, what is it that caused skeletal details, shadows of plants, etc. to show up?
Cheers!