Barbet was one of the first to confront the idea that fresh liquid blood, which he guessed would spread out and soak in around its source by capillary action was not an appropriate medium for making the well defined edges of the trickles on the arms and across the back. Perhaps he tried dribbling blood on a sheet, perhaps he tried blotting it with cloth; I don't know, but whatever it was, he failed. He was also aware that blood dries surprisingly quickly, and that it doesn't flow well from dead bodies, which again could not account for the trickles. However, he was unable to let go of the idea that the stains are really blood, so had to speculate, and the exudate was born. Trouble was, exudate, as well he knew, is yellow to colourless, and the marks he was trying to explain are red. The solution to that was that the red blood cells had largely hemolysed, and their content spread out into the plasma. He hoped that by a process similar to chromatography, the serum would spread out further than the red colour, and imagined he could identify serum borders to the wounds. As far as I know, nobody checked whether this was a credible hypothesis by lifting a dressing off a clotting wound to find out what had happened, and hypothesis became gospel first by authority and then by antiquity. Some rather gruesome images found by Googling "wound dressing removal" show what happens, and the marks look nothing like those on the shroud. As far as I know the Lavoies were the first to carry out reasonably appropriate experiments (in Blood on the Shroud of turin: Part II, http://www.shroud.com/pdfs/ssi08part3.pdf
). They found that in fact whole blood does not seep out into the surrounding cloth at all well. Blood was placed on clear plastic, allowed to dry for half an hour, then held vertically with cloth taped against it. A trickle seeped downwards, carrying red colour, but the clot itself transferred remarkably intact. However if the cloth was not taped against the clot for an hour or so, the serum dried faster than the rest of the blood, and although the clot itself transferred quite well, the serum did not. This is almost exactly the opposite of the action postulated by Barbet. Interestingly, a good blood clot image was produced even four hours after the fresh blood was allowed to dry, but in this case, it simply rested on the cloth, and could be "removed" in its entirely without leaving a stain.
The experiment was repeated, moistening the blood before application of the cloth. This time there was considerably more seepage around the edges of the clot. Even so, if the cloth was applied after four hours of the blood being placed on the plastic, the moisture did not soften the clot sufficiently for any permanent stain to form on the cloth.
It is clear that 'clot retraction exudate' is not required for a neat transfer of a fresh blood pattern, without seeping round the edges, onto cloth. It is also clear that after three or four hours drying no permanent stain is formed, even if the blood is moistened beforehand. Dried blood from previous wounds (scourging, and possibly the trickles) would produce no stain. From their position as believers in the authenticity of the shroud, the Lavoie's conclude: the bloodflows "all had one thing in common: all were actively flowing near the time of death." While authenticists have to argue about this, as the wounds, from scourging and crowning to the spear through the side clearly occurred at very different times, the forger theory finds no problem at all, as he could easily have dribbled his blood (assuming, for this comment, that it is blood) wherever he wanted within a hour or two of drawing it from its source.
Adler speculates that a forger could not have painted the blood on, as he would need "a constant supply of fresh blood exudates." I would modify that to "a constant supply of fresh blood." However he does not notice that this would have been much easier for a forger to acquire (perhaps with the help of a professional blood-letter), than for an actual dead body to supply. Adler goes on to say that a forger would then have to "paint a serum contraction ring about every wound." This doesn't make sense. If the marks were made by some sort of exudate, then the serum ring would form as naturally around an artificially applied mark as about a naturally transferred one. In fact, as the UV photos have shown, the amount of serum (if that's what it is) is negligible.
What on earth does this mean? I think it refers to the fact that when the image of the shroud is submitted to a brightness/height conversion program, such as the famous VP8 image analyser, or the more convenient ImageJ, some of the blood-stains do not appear appropriately correlated with the shape of the body, as if they had been painted in the wrong place. Rather than assuming they were, in fact, painted, in the wrong place, various convoluted explanations have been suggested that the cloth was originally placed quite tightly around the arms and face, collecting bloodstains from the sides of the arms, and face, and was then stretched more flatly, so that a more or less planar body-image can be formed. There have been several examples of this, each concentrating on explaining particular aspects of the hypothesis, but none noticing those aspects of it which disagree, and all somewhat differing from each other. In particular they have been used to explain the trickles in the hair (the blood was down the cheeks, but when the cloth was flattened out the image of the hair appeared around it), and the off-arm blood flows (the cloth was wrapped around the arm to collect the blood, then flattened out above it to collect the image), but do not explain the absence of blood on the 'sides' of the legs, which would surely have appeared if the cloth had been wrapped around them in the same way as it was around the arms.