For almost 200 years, archaeologists have been puzzled by a mysterious brown stain found on ancient fragments from the Parthenon temple in Greece. Scientists from the University of Southern Denmark recently conducted new analysis, but the mystery remains unsolved.

In the National Museum of Copenhagen, there is a marble head that was once part of the Parthenon in Athens. The head was from a statue depicting a centaur, a mythical half-man half-horse creature, in a battle scene. For unknown reasons, parts of the centaur head are covered by a thin brown film, similar to other Parthenon marble fragments.

The British Museum first examined the brown stain in 1830. They tried to figure out if it was from ancient paint but decided it was probably from a chemical reaction with air or iron particles in the marble migrating to the surface and turning it brown. Since then, scientists have studied the stain many times but still don’t know what caused it.

In 1851, the chemist Justus von Liebig did the first real scientific test. He found the brown film contained oxalate salts from oxalic acid. Later studies confirmed this. But no one knows where the oxalates came from. Professor Kaare Lund Rasmussen and his team from the University of Southern Denmark wanted to see if a living thing like algae, bacteria, fungi or lichens could have made the stain. Others had suggested this before but no specific organism was identified.

Vista frontal y posterior de la cabeza, con la mancha claramente visible
Front and back view of the head, with the stain clearly visible | photo National Museum of Denmark

The centaur head came to Denmark in 1688 as a gift. It was brought by a Danish captain after the Parthenon was damaged by bombing in Athens. The head has been displayed at the National Museum in Copenhagen since it was put in the Royal Collection.

For their research, the team took five small samples from the back of the centaur head. Tests at the university included protein analysis and a technique called laser ablation inductively coupled plasma mass spectrometry. They found no traces of living things, only modern fingerprints and maybe an old bird egg smashed on the marble long ago. This makes the living organism theory less likely now. Evidence of ancient paint was not found either.

Through their analysis, the team discovered the brown film has two separate layers about 50 micrometers thick with slightly different chemical compositions. Both layers contain the minerals weddellite and whewellite, oxalate salts. The two layers contradict theories that the stain came from materials migrating from inside the marble or air reactions.

Because the stain has two distinct layers that are chemically different, it’s probable they came from separate sources. This could suggest painting or preservation treatments were applied. But without traces of those substances, the cause of the brown stain remains a mystery. Even after many investigations, the centuries-old puzzle persists.

Sources

University of Southern Denmark | Rasmussen, K.L., Rasmussen, B.B., Delbey, T. et al. Analyses of the brown stain on the Parthenon Centaur head in Denmark. Herit Sci 12, 18 (2024). doi.org/10.1186/s40494-023-01126-9

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