This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.
Salt is the largest single group of alchemical substances in this taxonomy, twelve mineral salts that range from the entirely familiar to the genuinely exotic. Three of them form a clear sub family by color and by the metal each one carries: Blue Vitriol is a hydrated copper sulfate, Green Vitriol a hydrated iron sulfate that also supplied the iron gall ink behind most of Europe's written records, and White Vitriol a hydrated zinc sulfate, the one vitriol with no fixed planetary attribution because zinc itself was never one of the seven classical metals. Alum and Borax were both commercially significant imports, Alum controlled as a strategic resource at sites such as Tolfa for its unmatched power as a dye mordant, Borax carried from Tibetan lake deposits and prized by goldsmiths as a flux long before its chemistry was understood.
Common Salt's own entry draws a distinction worth carrying into the group as a whole: it should not be confused with the Paracelsian principle Salt, one of the tria prima, a philosophical category for the fixed, incombustible residue of any burned body that shares the name without being identical to table salt itself, the same kind of name shared between a literal substance and a broader philosophical principle seen elsewhere in this atlas with Sulfur. Saltpetre and Tartar round out the group by origin rather than composition, Saltpetre scraped from cellar walls as the essential ingredient of gunpowder and of Aqua Fortis, Tartar and its derivative Salt of Tartar drawn from wine casks rather than from any mine, while Glauber's Salt stands apart as the one member with a named discoverer, Johann Rudolph Glauber, who documented it himself in the mid seventeenth century.