Christian tradition has three stories about Bartholomew's death: "One speaks of his being kidnapped, beaten unconscious, and cast into the sea to drown. Another account states that he was crucified upside down, and another says that he was skinned alive and beheaded in Albac or Albanopolis", near Başkale, Turkey. The account of Bartholomew being skinned alive is the most represented in works of art, and consequently Bartholomew is often shown with a large knife, holding his own skin (as in Michelangelo's Last Judgment [below]), or both. Bartholomew is also the patron saint of tanners.
Sculpture by Marco d’Agrate, 1562 (Duomo cathedral, Milan-Italy). Image from detail-detail-detail via The Oddment Emporium.