"This is the hand of the philosophers with their seven secret signs, to which the ancient sages were bound.
The thumb: Just as the thumb powerfully closes the hand, so does saltpetre do in art.
The index finger: Next to saltpetre, vitriol is the strongest salt. It penetrates all metals.
The middle finger: Sal ammoniac shines through all metals.
The ring or gold finger: Alum gleams through the metals. It has a wonderful nature and the most subtle Spiritus.
The ear finger: Common salt is the key to art.
The palm: The fish is Mercury, the fire Sulphur. "
J.I.Hollandus, Chymische Schriften, Vienna, 1773