The Seven Metals and Their Companions: Elements the Alchemists Knew

The alchemists called it Sol, the metal of the Sun, and made it the target of chrysopoeia, the gold-making project. It is almost chemically inert and does not tarnish, and only aqua regia, one part nitric acid to three of hydrochloric, will dissolve it.

Luna, the metal of the Moon, ranked second to gold in the classical hierarchy. The association is with whiteness and the lunar month, and survives in lunar caustic, the old name for silver nitrate.

Iron was the alchemists' Mars, marked with a circle and an arrow, and the link lives on in the words martial and the red planet and in red rust. Its page also records that iron-56 sits at the peak of nuclear binding energy, which is why stellar fusion stops there.

The only metal liquid at ordinary temperature, and the alchemists' most important substance. It is both the planet and the god, and for Paracelsus it was one of three principles, standing for volatility. Its ore cinnabar gives up the metal directly when roasted.

The metal of Jupiter, alloyed with copper to make bronze, and the reason for some of the earliest long-distance trade in Europe, out of Cornwall and Iberia. Its page also records tin pest, the crumbling of cold tin into grey powder, once blamed on the devil.

In alchemy copper is Venus, marked with a circle above a cross, a link usually traced to polished bronze mirrors and the green of corrosion. Its Latin name cuprum comes from aes cyprium, the metal of Cyprus.

The alchemists' Saturn, the heaviest and dullest of the seven, whose association survives in the word saturnine and in saturnism, the old name for lead poisoning. It is also the end point of the uranium and thorium decay chains, so transmutation runs from heavy elements toward lead rather than the other way.

Brimstone, found native around volcanic vents. In Paracelsus's tria prima of sulfur, mercury and salt it stood for combustibility rather than for the yellow powder itself, and its alchemical mark is a triangle above a cross.

Known to the alchemists through orpiment, whose Latin name means gold pigment, and scarlet realgar, both used as pigments and both poisonous. Albertus Magnus is generally credited with isolating the element around 1250, and the Marsh test of 1836 finally made it detectable in the body.

Known since prehistory as charcoal and soot, and used constantly in alchemy as a reducing agent, yet never counted among the planetary metals. Lavoisier showed in the 1770s that diamond and charcoal burn to the same gas, a closing reminder that the alchemists' list was not the chemist's.