The section on alchemysts focuses primarily on efforts to turn base metals into gold. Mackay notes that many of these practitioners were themselves deluded, convinced that these feats could be performed if they discovered the correct old recipe or stumbled upon the right combination of ingredients. Although alchemists gained money from their sponsors, mainly noblemen, he notes that the belief in alchemy by sponsors could be hazardous to its practitioners, as it wasn't rare for an unscrupulous noble to imprison a supposed alchemist until he could produce gold.

https://en.m.wikipedia.org/wiki/Extraordinary_Popular_Delusions_and_the_Madness_of_Crowds