The Net, in alchemy, is an alloy of copper and iron, whose crystal structure induces a network pattern on its surface. It was described in the 17th century by Sir Isaac Newton.
Newton produced the substance by following what he regarded as a recipe, encoded in classical mythology, for part of the process of achieving the philosopher's stone. The relevant myth involved the god Vulcan finding his wife Venus (alchemical symbol for copper) in bed with the god Mars (alchemical symbol for iron)
Newton's interpretation rested on typical alchemical associations, construing Vulcan as a stand-in for fire, Venus for copper, and Mars for iron; Vulcan, the craftsman of the gods, having made a metal net for the purpose of hanging the adulterous couple from a high ceiling, Newton saw the use of iron to reduce antimony sulfide at high temperature to antimony regulus, and combining it with copper to produce the "network" on the alloy, as fulfilling the real meaning of the story.
George Starkey described his own synthesis of the Net after Newton and created a theory like Newton's, of mythological tales as secret alchemical codes.