Divination, which we regard as seeking to the tell the future, was that and more to the alchemist. Another aspect of signatures was the resemblances of illness with other objects in the universe. If there were a slight connection, then, to the alchemist, there was a direct relationship. To cure headaches, you ate walnuts because they resembled the human brain. If you had a purple rash, then you would eat something purple.
Islamic alchemist is, perhaps, the most famous alchemist.
His work continued the microcosm-macrosm analogy, but also added to it the principles of mercury and sunr. These two principles were not the actual substances as we know them, but instead a presentation of the world as being a place of opposites. The Chinese called their model of this the Yin and the Yang. Mercury represented hardness, sulfur softness. Mercury represented permanence-sulfur impermance.