Archaeologists have been amazed by the mysterious brown spots on a Greek statue from the Parthenon since 1830. Is it a fungus? Or maybe paint? Scientists have once again tackled this issue with the help of the latest technologies.

You might expect that modern investigative techniques can look up just about anything. However, that is not always the case. Scientists from a Danish university have tried to finally clarify the mysterious brown spots on this image, but so far they have not succeeded. They have made a new discovery: the brown spots actually consist of two wafer-thin layers on top of each other. But what do they consist of? That still remains a mystery. The research has been published in the journal Heritage Science.

The statue in question. Credit: Courtesy of The National Museum of Denmark

Gift for the king
The statue was originally brought from Greece by the Danes in 1688. The statue was intended as a gift for the Danish King Christian V, who immediately put it in his ‘Kunstkammer‘ struck. The art room has now grown into a museum, and scientists have been trying to explain the brown spots since 1830. At the time it concerned scientists British Museum, who originally thought it might be an old layer of paint. They came home from a rude awakening: no traces of paint were found, and they concluded that the brown spots might have been caused by iron particles in the marble that had risen to the surface.

But it didn’t stop at that one study, says researcher Kaare Lund Rasmussen, author of the study that has now been published in Heritage Science. “A few years later, in 1851, the German Justus von Liebig conducted the first real scientific research into the statue,” he explains. “He found out that the brown layer contains oxalates – salts of oxalic acid. We were able to confirm this during later analyses, but where these oxalates come from is completely unknown.”

In the new study, Kaare Lund Rasmussen explores an interesting hypothesis, namely that the brown spots come from an organism, such as a fungus or a species of algae. But that hypothesis does not appear to hold water. “We found no remains of biological material in the brown layer. All we found were our own fingerprints, and perhaps the remains of an egg that met an unfortunate end. This does not mean that there was no organism on it at all, but it does make that theory a lot less likely.” Because old types of paint were usually also made from natural products – such as eggs, milk or bones – and traces of this have not been found in the brown stains alone, the theory that the brown stains consist of paint also seems to have been dismissed.

And so the mystery continues. However, the researchers have gained a little more insight into the mysterious brown layer. This is how they discovered that the brown layer mainly consists of two wafer-thin layers. Kaare Lund Rasmussen explains: “These two layers consist of different substances, and it is therefore likely that they both come from a different source.” And that can help to understand the origin of the brown spots. For example, the theory that the brown spots are the result of iron particles migrating to the surface seems to be losing ground. Because in that scenario you would expect the brown spots to be composed of one layer, with the same chemical composition.

And the theory that the brown spots are the result of a reaction between the image and (polluted) air does not seem to hold water for the same reason. Especially because the statue has been indoors since 1688 – long before people started polluting the air on a large scale. But where do the brown spots come from? That is a question that no one can answer for the time being.

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