The most striking thing about Bartholomew in Western art is that he is usually holding his own skin. Michelangelo painted him that way in the Sistine Chapel, and the flayed hide, with a face said to be the artist's own, is one of the best-known details in the fresco. Milan cathedral has a sixteenth-century statue of him carrying his skin over his shoulder like a garment.
None of this is in any early source. The flaying enters through late apocryphal acts and the medieval compilations that drew on them, above all the Golden Legend of Jacobus de Voragine in the thirteenth century, which gathered the martyrdom traditions into the form that fixed them for European art. Even there the accounts do not agree: some have him flayed and then beheaded, some crucified, some beaten. The Armenian tradition, which claims him as a founding apostle alongside Thaddaeus, places the death at Albanopolis in Greater Armenia.
The mission fields are similarly various and mutually exclusive. Eusebius, in the early fourth century, reports that the philosopher Pantaenus found in India a Hebrew copy of Matthew said to have been left by Bartholomew, which is the earliest surviving claim about his travels and is itself a report of a report. Other traditions send him to Mesopotamia, Persia, Ethiopia or Lycaonia. These are not variants of one memory; they are separate local claims, each attaching an apostle to a church that wanted one.
The honest position is that nothing is known about what he did or where he died, and that the skin is iconography.