The face cloth is called the "Sudarium of Oviedo". It's history can be seen here:
https://www.shroud.com/guscin.htm
There are a couple of key things that can be learned from this item.
1. The chain of custody is well documented as coming from Jesus crucifixion.
2. The stains indicate the face was upright when the man died.
3. The stains are one part blood and six parts pleural oedema indicating the person died of asphyxiation.
4. There are several stains indicating the face cloth was put on while the person was on the cross, an hour later they were laid down on the ground, about 45 minutes later they were lifted from the ground.
5. At the time of death when the cloth was first put on the head was tilted 70 degrees forward and twenty degrees to the right, indicative of a person who has been crucified.
6. Pollen taken from the Sudarium supports the historical account of the Sudarium first being in Jerusalem, then North Africa, Toledo and Oviedo.
7. Residue of myrrh and aloe were found.
8. the cloth has no artistic or monetary value. Keeping this cloth, taken from the tomb of a crucified person, is indicative of its authenticity.
Apparently Jewish tradition is that if the face of a dead person has been disfigured it should be covered, however you would not bury the person with the face covered, so the cloth presumably covered the face till he was put in the tomb and then removed.