Michael Maier’s Medicament Coelidonia – A Possible Explanation of its Composition and Production

The composition and way of production of Michael Maier's medicament Coelidonia, mentioned in his book <i>De Medicina Regia et verè Heroica, Coelidonia,</i> were inferred from indications in Maier's book <i>Viatorium, hoc est, de montibus planetarum septem eu Metallorum</i>. The substance was synthesized by the author in a modern laboratory. It is a lead oxychloride of brilliant yellow colour with a composition of approximately Pb₇O₆Cl₂. The same substance was produced from the 1780s to at least 1825 as a pigment under the names of Patent Yellow, Turner's Yellow and Casseler Mineral-Gelb (Cassel Mineral Yellow).