PLUTARCH'S REPORT ON THE BLUE PATINA OF BRONZE STATUES AT DELPHI: A SCIENTIFIC EXPLANATION
WALTER A. FRANKE, & MAGDA MIRCEA
2 BACKGROUND RESEARCH
Plutarch was an important official in the hierarchy of Apollo's temple at Delphi for 30 years, and he played a notable part in the revival of the shrine in Trajanic and Hadrianic times (Flaceli�re 1943, 1987; Barrow 1967). A recent groundbreaking discovery made by an American multidisciplinary team provided evidence that he was indeed a reliable eyewitness and a most valuable ancient source on the Delphic Oracle. The “sweet smelling exhalation” that he mentioned really existed and was an emission of light hydrocarbon gases generated in the underlying strata of the bituminous limestone of Delphi (De Boer and Hale 2000; De Boer et al. 2001; Spiller et al. 2002).
Plutarch (1935) began his work The Oracles at Delphi No Longer Given in Verses by noting the impressions of a young man, Diogenianus, who made a tour of the Delphic sanctuary: “The appearance and technique of the statues had only a moderate attraction for the foreign visitor, who, apparently, was a connoisseur in works of art. He did, however, admire the patina of the bronze, for it bore no resemblance to verdigris or rust, but the bronze was smooth and shining with a deep blue tinge, so that it gave an added touch to the sea-captains [he had begun his sightseeing with them], as they stood there with the true complexion of the sea and its deepest depths” (260–61). Another speaker, named Theon, suggested an explanation for this uneven color of the bronze: “It is air alone; we have most reason to believe that the air occasions it and from its constant presence and contact the bronze here gets its exceptional quality” (Plutarch 1918). Theon proceeded to describe the air from Delphi, which has intriguing features, as
dense and compact, possessing a certain vigour because of the repulsion and resistance that it encounters from the lofty hills; and it is also tenuous and keen … so the air, by reason of its tenuity, works its way into the bronze and cuts it, disengaging from it a great quantity of rust like dust, but this it retains and holds fast, inasmuch as its density does not allow a passage for this. The rust gathers and, because of its great abundance, it effloresces and acquires a brilliance and lustre on its surface. (Plutarch 1935, 267)
In the last decade of the 19th century, archaeologists noticed that there might be a link between Plutarch's report and the surface coloration of some archaeological bronzes discovered in Delphi and elsewhere in Greece. Villenoisy (1896, 70) suggested this blue patina could have been produced by “oxidation, ” since the atmosphere at Delphi is “ozone-rich.” Chaplet (1936) agreed that Plutarch's description of the bronzes at Delphi was consistent with the favorable mountain climate of this region. Moreover, Bourguet (1914) believed that it was the arid atmosphere of Delphi (“l'air sec de Delphes”) that turned the Charioteer's color to green-blue within only a few days of outdoor exposure.
The archaeological controversy that has centered on this passage concerns the question of whether all the bronze statues in the sanctuary had the same peculiar patina or only the statues of the Spartan Monument (Pouilloux 1965; Bommelaer 1971; Jouanna 1975). In the past decade a comprehensive review of the studies related to Plutarch and his connection with Delphi has concluded that almost nothing remained to be said on the blue patina of bronze statues at Delphi: “Il semble qu'il n'y ait plus rien � ajouter sur la patine du bronze � Delphes” (Zagdoun 1995, 589).
The present study aims to combine a new study of classical literary sources with the developments of natural science in a theoretical attempt to find a scientific explanation for a blue bright patina on the bronze statues, as well as to determine the circumstances under which it might have been formed at Delphi in ancient times.
The problem resembles an equation with two vari-ables: the nature of the blue compound of the patina and the specific environmental conditions that could produce and maintain it on the surface of the bronze statues.
To solve the problem, it is necessary to analyze the general environmental conditions at Delphi; review the colors of possible copper patina minerals to select the blue ones; and test whether the selected blue patina mineral is thermodynamically stable under the environmental conditions inferred for ancient Delphi.