This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.
Metal Preparation gathers nine members built around the seven classical metals of alchemy, each paired in the tradition with one of the seven visible planets. Gold answers to the Sun, Silver to the Moon, Copper to Venus, Iron to Mars, Tin to Jupiter, Lead to Saturn, and Quicksilver, alchemical mercury in its literal liquid form, completes the set without a single fixed planetary partner of its own, since the philosophical principle Mercury it lent its name to was understood as broader than the metal alone. Gold sat at the top of this hierarchy as the most perfect metal and the Great Work's ultimate goal, Lead at the bottom as the raw material the whole transmutational program aimed to carry upward, and each metal's planetary symbol, a circle for gold and the sun, a crescent for silver and the moon, and so on, is shared directly with its astrological glyph, the clearest visual evidence of how tightly the two systems were bound together.
Two members sit outside that sevenfold scheme. Amalgam is not a metal at all but the soft alloy mercury forms with another metal, most importantly gold or silver, which underpinned the fire gilding technique used to fuse a thin layer of pure gold onto a base object. Arsenic is the group's other exception, a brittle, metallic looking element usually meant, in ordinary pre-modern speech, as the toxic white oxide rather than the element itself, and never assigned a fixed place among the seven planetary metals at all.