Why does it matter? Well, as a recent post/article (here?) pointed out, many Christians don't believe in Christ because of their faith (~ belief in things that can't be proven), but rather because they feel they have evidence to point to the truth of their belief. They've talked with God or seen miracles, etc., personally. When the shroud was seemingly conclusively shown to be from the Middle Ages, the belief of some must have been shaken. If it were shown to be from ~ 30 AD, many people would take it to be evidence of the truth of the Gospels.
How was it formed? Well, I think people have a pretty good [link|http://www.freeinquiry.com/skeptic/shroud/as/schafersman.html|idea]. (It's a bit strident.):
[...] I also want to comment briefly on a number of other topics concerning the authenticity of the Shroud of Turin. First, Walter McCrone [16] found artist's red ochre (iron oxide) pigment particles covering the image area and both red ochre and vermilion (mercuric sulfide) pigment particles in the blood areas, but none of these particles on tape samples from the off-image areas. This evidence was sufficient for any objective and rational person to accept the fact that the Shroud was an artistic representation of the Shroud, and not the real thing. But McCrone was illogically and unjustifiably criticized by STURP participants and other advocates of authenticity, who then and now attempt to clumsily explain away the plain and obvious evidence of artifice that he first discovered. Walter McCrone recently summarized his results again in this journal [17], so I will not repeat them again.
[...]
Such explanations are pseudoscientific attempts to keep the possibility of authenticity alive in the minds of supporters who lack the ability to think critically. There is no blood on the Shroud: all the forensic tests specific for blood have failed [18] (although some investigators [19] unrigorously concluded that blood was present after conducting numerous forensic tests for iron, protein, albumin, etc., which came up positive because these materials are indeed on the Shroud in the form of tempera paint). Old blood is not bright red, and no amount of bilirubin [20] can explain that away. Real blood mats on hair, and does not form perfect rivulets and spiral flows. Real blood does not contain red ochre, vermilion, and alizarin red pigments. Real blood and its organic derivatives have refractive indices much less than red ochre or vermilion, and they can be easily distinguished using Becke line movement under a light microscope. McCrone's examination of the red particles on the Shroud samples revealed no blood or blood derivatives.
Schafersman even addresses (in 1998) Rogers' 2004 arguement that samples were taken from the wrong bit of the shroud:
The Shroud's Medieval Radiocarbon Date
Without question, the most spectacular refutation of the authenticity of the Shroud of Turin was the determination that the linen on which the image lies dates from approximately 1325. The Shroud was sampled and the dates determined by the most scrupulous and scientifically-valid techniques and procedures that are possible. Sampling was carefully conducted and witnessed, the samples were properly cleaned and prepared, and three different laboratories performed the 14C dating using blind control samples in addition to the Shroud samples. All the dates were consistent among the labs. Since Robert E. M. Hedges has reviewed the radiometric dating analyses and results in this journal[24], I need not repeat them here. I merely want to state that the quality of the radiometric data are so rigorous that no objective, rational person can reasonably deny them.
Naturally, believers in the Shroud's authenticity have thrown up numerous criticisms that are variously ludicrous, vacuous, and without merit. Contrary to pro-authenticity advocates, the linen samples were not deceptively switched, not taken from the wrong part of the Shroud material, not improperly cleaned and prepared, did not have a bioplastic coating, were not contaminated by modern bacteria and fungi that were not removed, the carbon-14 content of the cloth was not altered by the fire of 1532, the final results were not deliberately falsified by a conspiracy of anti-religious scientists, and so forth. As has been pointed out by others, modern material of approximately twice the mass as the Shroud samples would have to be added to the samples to bring authentic first-century linen up to radiocarbon dates of the fourteenth-century, and this would have been just too obvious to go unnoticed by so many independent investigators. Once again, the ad hoc excuses, criticisms, and counter-arguments of the radiocarbon dating by Shroud enthusiasts were put forward to preserve appearances at any cost, a classic characteristic of pseudoscience. In real science, legitimate and reliable data that falsify one's most treasured hypotheses and beliefs are accepted, and lead one to abandon one's former beliefs. But sindonology is a pseudoscience, not real science.
I think the preponderance of the evidence points to it being made in Europe in the Middle Ages.
I think the shroud is interesting for 2 reasons: 1) it's an interesting scientific puzzle; 2) it's an interesting experiment in mass psychology.
I think it's yet another example of "Where you stand depends on where you sit." I.e. it's very difficult for people to overcome their biases, their upbringing, what they learn from their circle of friends.
My $0.02.
Cheers,
Scott.