Contrary to what many people might think, the Church's teaching and alchemical methods are not mutually exclusive. In fact, many renowned alchemists were priests and monks, like the Dominican friar Albertus Magnus, or the Franciscan Roger Bacon, who, if legends are to be believed, created a talking brass head.
Unfortunately, though, charlatans also try to associate themselves with this mysterious art. And sometimes it's hard to tell a true scholar from a fraud. Take the Aragon kings's personal physician, Arnaldus de Villanova. First he was imprisoned and accused of heresy (that heresy being mainly proposals of church reforms). He was then saved by the Pope himself, whom he had previously cured of a serious illness. But then another Pope imprisoned Arnaldus again and his works were ordered to be burned. So what are we to think of Arnaldus, in the end?