The Catholic Church has neither formally endorsed nor rejected the shroud, but in 1958 Pope Pius XII approved of the image in association with the devotion to the Holy Face of Jesus. Pope John Paul II called the Shroud "a mirror of the Gospel". Other Christian denominations, such as Anglicans and Methodists, have also shown devotion to the Shroud of Turin. Diverse arguments have been made in scientific and popular publications claiming to prove that the cloth is the authentic burial shroud of Jesus, based on disciplines ranging from chemistry to biology and medical forensics to optical image analysis. In 1988, three radiocarbon dating tests dated a corner piece of the shroud from the Middle Ages, between the years 1260 and 1390. Some shroud researchers have challenged the dating, arguing the results were skewed by the introduction of material from the Middle Ages to the portion of the shroud used for radiocarbon dating. However, all of the hypotheses used to challenge the radiocarbon dating have been scientifically refuted, including the medieval repair hypothesis, the bio-contamination hypothesis and the carbon monoxide hypothesis.