Was the apostle John boiled in tar?

In an unlikely Christian tradition, the apostle John was sentenced to be boiled in oil, but survived without injury. He was then exiled to the island of Patmos, where he wrote the Book of Revelation, which was first attributed to him late in the second century. However, the existence of a tradition such as this does not mean it really happened.

The story raises questions such as why boiling in oil was chosen, other than because it was possible to imagine John escaping unscathed, as could not be imagined in the case of beheading, spearing or crucifixion. Why was John apparently not tortured and permanently disabled before being placed in the oil? If the oil did not work, why was he then exiled rather than simply being speared or crucified? How did they manage to exile John? If he was immune to harm, the soldiers could not have forced him to accompany them to Patmos.

The story of John being boiled in oil and exiled to Patmos is an extreme example of the literary technique of hagiology that began with Acts of the Apostles and developed over the early centuries of Christianity. Its primary purpose was the veneration of saints, with a secondary purpose of explaining how John came to write Revelation, as was by then supposed.