Zosimus of Panopolis, of the end of the third and beginning of the fourth century AD, was a Gnostic Christian and probably the most important of the Alexandrian alchemists.
[taken from a collection of magical charms and prescriptions]:
Dry the substance then in the Sun and preserve it as a mystery not to be revealed, which none of the sages ventured to communicate by word but only by signs. For it is an indication of this that in their esoteric writings they use the word stone for that which is not a stone, the unknown they describe as universally known, the dishonoured as highly honoured, the ungenerous as divinely bountiful. Let me then also extol heaven's real gift, which alone in our daily experience rises above the material; for this is the medicine that is potent to heal, the Mithraic mystery.