The Shroud of Turin
The image on the shroud is much clearer in black-and-white negative than in its natural sepia color. The negative image was first observed in 1898, on the reverse photographic plate of amateur photographer Secondo Pia, who was allowed to photograph it while it was being exhibited in the Turin Cathedral. In 1978 a detailed examination was carried out by a team of American scientists called STURP. They found no reliable evidence of forgery, and called the question of how the image was formed "a mystery".
In 1988, a controversial radiocarbon dating test was performed on small samples of the shroud. The laboratories at the University of Oxford, the University of Arizona, and the Swiss Federal Institute of Technology, concurred that the samples they tested dated from the Middle Ages, between 1260 and 1390. Three peer-reviewed articles have since been published contending that the samples used for the dating test may not have been representative of the whole shroud.
Scientific and popular publications have presented diverse arguments for both authenticity and possible methods of forgery. A variety of scientific theories regarding the shroud have since been proposed, based on disciplines ranging from chemistry to biology and medical forensics to optical image analysis. According to former Nature editor Philip Ball, "it's fair to say that, despite the seemingly definitive tests in 1988, the status of the Shroud of Turin is murkier than ever. Not least, the nature of the image and how it was fixed on the cloth remain deeply puzzling". The shroud is one of the most studied artifacts in human history, and one of the most controversial.