Sudarium

[…] Watt, faithful to his rule, took no more notice of this aggression than if it had been an accident. This he found was the wisest attitude, to staunch, if necessary, inconspicuously, with the little red sudarium that he always carried in his pocket, the flow of blood, to pick up what had fallen, and to continue, as soon as possible, on his way, or in his station, like a victim of mere mischance.

This cloth, known as the Veronica or the vera icon, was kept in St. Peter's in Rome, where its presence is documented with some certainty from the mid-twelfth century onward. At first, however, the existence of the Veronica was recorded not as an image but as a textile, a sudarium.

Most interestingly, scientific analysis has shown that the stains of the sudarium match those on the head portion of the Shroud, a notion first suggested by Monsignor Ricci in 1965.