Stephen E. Jones does not disappoint with his newest, very comprehensive and thoroughly useful addition to his series, "The Shroud of Turin." Entitled "3.3. The man on the Shroud was scourged," it is part 21 of the evolving series.
Problems for the forgery theory The scourge marks on the Shroud are physiologically accurate. When examined under a microscope, each scourge mark reveals a slightly depressed center and raised edges. Under ultraviolet light each scourge mark can be seen to have a "halo" of lighter colour surrounding it. These halos were chemically tested and found to be blood serum which is left behind after a blood clot forms and then retracts inwards as it dries, a process called syneresis. These scourge mark indented centres and raised edges on the Shroud are not visible to the naked eye, but can only be seen when examined under a microscope and the serum halos can only be seen under ultraviolet light. This is further evidence that the Shroud could not have been created by an artist in the Middle Ages because that knowledge about blood clot structure, let alone a microscope and an ultraviolet light source to see them, did not then exist for many centuries into the future.
and he quotes Thomas de Wesselow:
"Once again, though, it [the Shroud] differs dramatically from anything envisaged in the Middle Ages. The vast majority of medieval images of the dead or dying Christ fail to depict any scourge marks at all … Christ is sometimes shown bleeding in depictions of the flagellation, but the effect is always rather crude. In Duccio’s rendering of the scene, for example, the scourge marks are represented as red dribbles all over the body, including the arms but not the legs …The artist displays no knowledge of the Roman flagrum, nor any conception of how it was wielded. Even a fifteenth-century artist as accomplished as Jean Colombe, who definitely knew the Shroud, was unable to reproduce its convincing pattern of scourge marks … To attribute the marks on the Shroud to a provincial unknown working in the mid fourteenth century is therefore ridiculous".
Read it. The choice of graphics is helpful.