How did they know how old the Shroud of Turin is?

Answer 1

The cloth now known as the Shroud of Turin first appeared about 1355 at a little church in Liry, in north-central France. According to a later bishop's report, written in 1389 by Pierre D'Arcis to the Avignon pope, Clement VII, the shroud was being used as part of a faith-healing scam. D'Arcis wrote of a predecessor who conducted an investigation which uncovered the forger: "Eventually, after diligent inquiry and examination, he discovered the fraud and how the said cloth had been cunningly painted, the truth being attested by the artist who had painted it, to wit that it was a work of human skill and not miraculously wrought or bestowed." So, from the earliest days of the Shroud, it was already known to be a recent creation, by the admission of the artist who painted it.

Tests in 1988, by three laboratories (at Oxford, Zurich, and the University of Arizona) used accelerator mass spectrometry to carbon-date samples of the linen. The results were in close agreement and were given added credibility by the use of control samples of known dates. The resulting age span was in the range 1250 to 1390 CE, consistent with the date of the reported forger's confession.