The correct answer to this open question is the following.
Besides using some measure of science, alchemists resorted to using magic to do what science seemed unable to accomplish.
One of the ancient practices of old magicians is alchemy. Although the concept brings ideas of mystery and old people with white beards wearing funny clothes, we can define Alchemy as the process to turn lead into gold. That's it. Since the Middle Ages, alchemists tried to combine science with magic in order to covert lead to gold. And all kind of stories has stemmed from these people.