26:17 · One of the alchemists' signs for nigredo or caput mortuum. Nigredo represented the epitomy of decline and decay, the starting point for the esoteric alchemists' work of transforming man into pure spirit, or symbolically, transforming an impure or base metal into pure gold, .
    This sign appears as a shield sign in a painting on a Greek vase from around 500 B.C.
    Like the preceding entry sign it could in the eighteenth century chemistry mean residuum, residue. It was also used for crocus metallorum, iron oxide.