A weight of 20th century carbon equaling nearly two times the weight of the Shroud carbon itself would be required to change a 1st century date to the 14th century (see It may interest skeptics to know that many people of faith believe that there is scientific evidence which supports their belief in the shroud's authenticity.
Of course, the evidence is limited almost exclusively to pointing out facts that would be true the shroud were authentic.
Avinoam Danin, a botanist from Hebrew University of Jerusalem claims he has identified pollen from the tumbleweed Gundelia tournefortii and a bean caper on the shroud.
He makes his complete case that the shroud is a medieval painting in Judgment Day for the Shroud of Turin (March 1999).
It is also claimed that the image is not a painting but a miraculously transposed image.
Skeptics believe that the shroud of Turin is just another religious relic invented to beef up the pilgrimage business or impress infidels.
It is claimed that there is type AB blood on the shroud. Blood has not been identified on the shroud directly, but it has been identified on sticky tape that was used to lift fibrils from the shroud. Other tests by Adler and Heller have identified it as blood.* If it is blood, it could be the blood of some 14th century person.
It could be the blood of someone wrapped in the shroud, or the blood of the creator of the shroud, or of anyone who has ever handled the shroud, or of anyone who handled the sticky tape.