PLUTARCH'S REPORT ON THE BLUE PATINA OF BRONZE STATUES AT DELPHI: A SCIENTIFIC EXPLANATION
WALTER A. FRANKE, & MAGDA MIRCEA
The Spartan Monument has not come down to our time. The same is true of all other life-size bronze statues from Delphi. Only the Charioteer survived because it was buried by a landslide more than 2, 000 years ago and was excavated in 1896. The Charioteer was rescued from the debris accumulated behind Ischegaon, an ancient retaining wall north of Apollo's temple (see fig. 1). According to recent geological analyses, the masonry of this wall shows a relatively thick coating of travertine (calcite) formed in situ over a period of time when spring waters ran downhill and splashed across the wall (De Boer and Hale 2000; De Boer et al. 2001). The presence of travertine is the main geological evidence for Ca-rich springs and enhanced CO2 degassing. In such geo-archaeo-logical conditions, the formation of azurite and malachite might be favored by intergranular soil solutions that may have elevated concentrations of the hydrogen carbonate ion, due to considerable concentrations of calcium hydrogen carbonate (Riederer 2003). The residue of the blue patina of this bronze is therefore presumably azurite that was developed during the burial time. It is unlikely that this statue had a blue patina before its burial because a considerably increased carbon dioxide concentration can hardly be assumed for its place in the upper part of the temple precinct (unless the statuary group was also enclosed by a wall). A thorough technical investigation of a cross section of the blue parts of the Charioteer would decide if the bluer shades are indeed made of azurite.
Thanks are due to Eva Logemann and Eveline Siegmann (Berlin) for their able help in preparing the figures. We would like also to thank Bea Hopkinson, prehistorian/researcher at University of California– Los Angeles, for having the kindness to proofread the English version, and for sharing with us her experience in resolving age-old artifactual evidence, or lack of it where materials do not survive time.