Moreover, the image on the Shroud is a photo-negative, as the Italian photographer Secondo Pia discovered in 1898. How would a medieval artist have created a perfect photo-negative image, given that photography was not invented until the early 19th century? By itself, this feature of the Shroud supports neither a medieval nor an ancient date of origin but rather reinforces the impression that, whenever or however the image was produced, the circumstances were remarkable.
Further mysteries abound. For example, the detailed image of the man rests only on the top two microfibers of the cloth, not penetrating the linen, as would paint or dye, and could be scraped away with a razor blade. The blood (type AB) seen on the cloth does fully penetrate the linen fibers, but tests show that it's separate from, and underneath the image. "Blood first, image second," is the catchphrase used by Shroud experts.