Litharge and minium are identified as two distinct lead oxide compounds related by the degree of oxidation: litharge is lead(II) oxide, PbO, and minium is lead(II,IV) oxide, more often written Pb3O4, a mixed valence compound containing lead in two different oxidation states within the same crystal structure, a genuine chemical subtlety that pre-modern craftsmen and alchemists could not have described in those terms even though they correctly recognized minium as the product of pushing litharge's own formation reaction further.
There is no real scholarly dispute over either identification, both compounds being well characterized and both still manufactured and used today, litharge chiefly in glass and ceramics and minium as a corrosion-resistant primer paint, though its toxicity has sharply reduced that latter use in recent decades. This entry treats litharge and minium together, as the historical sources themselves generally did, precisely because their relationship, two stages of the same roasting operation on the same starting metal, is itself the point worth preserving rather than obscuring by splitting them into two unrelated rows. Minium's use as a bright, corrosion-resistant primer paint continued in industrial and marine settings well into the twentieth century before its lead content led most jurisdictions to restrict it, a use that outlasted nearly every other alchemical-era pigment.