The year was 1687. The Holy League - a coalition formed by the Holy Roman Empire, the Republic of Venice, the Russian Tsardom and the Republic of the Two Nations (Poland and Lithuania) - was at war with the Ottoman Empire and its Tatar allies. , Cossacks, Moldavians, Transylvanians and Vlachs. It was not a world war, but almost.
Greece was, at that time, under Turkish rule and the Christian states were determined to recover it from the Muslim yoke. In September, the Venetian mercenary fleet was already anchored in Piraeus, ready to attack the enemy. The battle included an intense bombardment of the Acropolis, refuge of the Ottoman troops.
The Parthenon had been converted into a gunpowder depot so, when it was hit squarely by a shell, the catastrophe could not be avoided. The roof of the building, thirty columns and many of Phidias' sculptures were completely destroyed.
After the offensive, the Danish captain Moritz Hartmand climbed the Acropolis and took two marble heads, which were sent to Denmark in 1688 as a gift for King Christian V. They were kept in the Royal Kunstkammer, which later became the National Museum, where they have been exhibited since then.
One of the heads originally belonged to a centaur figure and was part of a scene depicting the battle of the Greek mythological Lapiths against the centaurs, the mythical creatures that were half-horse, half-human. And for unknown reasons, some parts of the head are covered with a thin brown film.
The mysterious film, which has also been found on other marble fragments from the Parthenon, was first examined by the British Museum in 1830. At that time an attempt was made to determine whether the color came from ancient paint, but it was concluded that that it could be the result of a chemical reaction with air, or that the marble contained iron particles that had migrated to the surface of the ground, staining it brown.
"There have been many attempts to explain the peculiar brown film. In 1851, the German chemist Justus von Liebig conducted the first real scientific investigation and determined that it contained salts of oxalic acid. This has been confirmed by later analysis, but the origin of oxalates remains a mystery," explains Professor Kaare Lund Rasmussen of the University of Southern Denmark.
As Rasmussen and his team explain in an article published in the journal Heritage Science, they took five small samples from the back of the centaur's head to subject them to protein analysis and so-called laser ablation inductively coupled plasma mass spectrometry.
"We especially wanted to examine - says the expert - whether the brown film could have been formed by some biological organism, such as lichens, bacteria, algae or fungi. This theory had already been suggested before, but no specific organism had been identified. The same occurs with the hypothesis based on the fact that they could be remains of paint applied, perhaps to protect or tone the surface of the marble.
The results of the study indicated that there were "no traces of biological matter in the brown layers, only our own fingerprints and perhaps a bird egg that was cracked into the marble in ancient times." This does not prove that a substance never existed. biological, but significantly reduces its probability.
It is also believed that it is difficult for the marble surface to be painted. Ancient pigments were usually based on natural products such as eggs, milk and bones, and no traces of such ingredients were found in the brown stain on the centaur head.
The scientists further discovered that the brown film consists of two separate layers with approximately the same thickness: about 50 micrometers each. They differ in the composition of trace elements. That there are two distinct layers goes against the theory that they were created by the migration of material, such as iron particles, from within the marble. It also contradicts the theory that they were the result of a reaction with air, specialists say.
Air pollution is also unlikely for another reason. The sculpture has been inside the National Museum in Copenhagen since before modern industrialization began in the 18th century. "As there are two brown layers with different chemical compositions, it is likely that they have different origins. This could suggest that someone applied paint or a conservation treatment, but since we have not found traces of such substances, the color remains a mystery," concludes Kaare. Lund Rasmussen.
