Wow, at 800 years old?
That’s an excellent question and I’m glad you brought that up! LOL
According to what I could find, the St. Bartholmew skinned alive was not the same one in the painting (the original Bartholomew). There was a St. Bartholmew (named after the apostle) who was said to have brought Christianity to Armenia. It was this Bartholmew who was “flayed” (skinned alive) and crucified upside down in the 8th century.