Plutarch's Report on the Blue Patina of Bronze Statues at Delphi: A Scientific Explanation

Abstract

Plutarch reported that the Spartan Monument from Delphi was coated with an unusual blue and glossy patina, due to peculiarities of the air inside the sanctuary. This bronze statuary group has actually vanished. The last remaining bronze sculpture from Delphi, the Charioteer, exhibited in burial a similar bluish appearance, which after a century of indoor exposure turned greenish. On visual inspection the lower torso still preserves a blue coloration. Professional conservators have not yet published any study on the Charioteer's patina. The present article integrates a new study of classical literary sources with knowledge of the natural sciences in order to find a chemical explanation for the blue patina, as well as the circumstances under which it might have been formed at Delphi in ancient times. The authors suggest that the the location of the sanctuary of Delphi above two active faults that break through limestone bedrock favored the formation of azurite on the surface of bronze statues in burial due to elevated concentrations of calcium hydrogen carbonate (e.g., the Charioteer), as well as in the open-air environment, under peculiar conditions (e.g., the Spartan Monument).