Copper

Copper was smelted from a range of ores, chiefly the carbonate malachite and the closely related azurite, in furnaces that reduced the ore's metal content with charcoal, a metallurgy old enough to define an entire archaeological period, the Copper Age, that in most regions preceded the later adoption of bronze and then iron. Copper is comparatively soft and ductile, easily worked cold or hot, and it takes a bright reddish luster that darkens and eventually turns green on long exposure to air and moisture, forming the same basic copper carbonate patina discussed under verdigris and malachite elsewhere in this atlas. Alchemically, copper was studied closely alongside its own vitriol, since dissolving copper in oil of vitriol or exposing it to acidic vapor yields blue vitriol directly, a transformation between metal and salt that alchemists watched as a visible demonstration of a metal taking on, and later potentially recovering from, a dissolved, salt form.

Beyond the laboratory, copper's practical importance as coinage metal, tool metal, and later as the essential ingredient of bronze and brass alloys made it one of the most economically consequential of the seven classical metals throughout the whole pre-modern period, its alchemical study never separate for long from its very practical, everyday uses across metalworking trades that had nothing directly to do with transmutation.

Copper's pairing with Venus is well attested across the alchemical tradition, and its symbol, a circle set above a cross, the same glyph still used today for the astrological sign and the biological symbol for the female sex, is consistently reproduced across historical sources with essentially no recorded variation.

The correspondence's origin is generally traced to copper's long association with Cyprus, the island whose ancient copper mines were significant enough in the classical Mediterranean economy that the metal's Latin name, cuprum, derives directly from Cyprus, and Cyprus itself carried a strong classical association with Venus, called Aphrodite in Greek, whose mythological birthplace and primary cult center were both said to be on the island. This is one of the clearer cases in the whole planetary metal scheme where the symbolic correspondence has a traceable geographic and mythological origin rather than resting purely on an abstract set of shared qualities, a point historians of alchemy including Lawrence Principe note as a useful example of how the seven metal, seven planet system drew on real classical geography and myth rather than emerging as a purely abstract philosophical scheme.