imageStephen Jones is up with with part 23, "3.5. The man on the Shroud was crowned with thorns," of his blog series, "The Shroud of Turin." He includes a wonderful quotation by Vignon:

Let us turn now to another wound, the reproduction of which would have required even greater ingenuity and skill. We allude to the large drop of blood visible on the forehead above the left eyebrow. This drop springs from a definite point, indicated by its darker colour … This dark point corresponds to one of the wounds made by the crown of thorns. The blood which has flowed therefrom has met in its course the two wrinkles of the forehead, and has, by this slight opposition, been forced to spread itself out, forming two small horizontal pools; thence it continued to flow, until it ended in a tear of blood close to the eyebrow, and having thus flowed, it dried upon the skin. Now any drop of blood, drying thus, upon a substance into which it does not penetrate, takes, when coagulated, a sort of basin-like shape, a section of which we give here … The border or brim of the basin is formed by the fibrine of the blood, containing the red corpuscles in its coagulum; the centre is composed of the serum, which in drying takes a dull brown tint. Here, as the liquid part of the serum evaporates, the convexity of the centre is depressed. The contour of the drop of blood preserves, however, the same shape as it had when it was fresh. Now this description applies exactly to the blood-drop on the forehead. In the parts where the blood has flowed, and where it has accumulated in sufficient quantity, it is bordered by a dark edge. The centre of the little stream, and the centre also of the terminal tear, are of a lighter tint. This drop of blood is reproduced not only with the greatest minuteness and delicacy, but with entire faithfulness to scientific detail. No painter, in his most elaborate work, has ever risen to such exactitude, as a glance at any of the numerous representations of Christ, Crowned with Thorns, will show us