Chemistry solves a French royal mystery

Scientists uncover who censored the 18th century letters of France’s doomed queen

X-rays reveal a hidden passage (at right) in a letter written by French Queen Marie Antoinette, dated January 4, 1792. The censored version is at right.

@CRC

Chemistry has solved a mystery that’s more than 200 years old: Who censored letters written by the Queen of France?

In the late 1700s, France was being torn apart by revolutionary war. Queen Marie Antoinette and the rest of the French royal family were arrested and imprisoned. They had tried to escape the country. Before she was executed , the queen exchanged secret letters with a rumored boyfriend. Someone later scribbled out the letters’ contents with ink.

an X-ray fluorescence scanner images one of Marie Antoinette's letters
An X-ray scanner analyzes the ink in a letter dated September 26, 1791. The letter was written by the French Queen Marie Antoinette to the Swedish Count Axel von Fersen.@CRC

Now, chemical analyses of the ink reveal the hidden words as well as the identity of the censor. Researchers reported the findings October 1 in Science Advances.

From June 1791 to August 1792, Queen Marie Antoinette managed to swap covert messages with Swedish Count Axel von Fersen. Whether the pen pals sent each other words of love or political secrets was a longstanding question.

Chemist Anne Michelin and her colleagues analyzed the letters using X-rays. The technique, called XRF, works by shooting an X-ray beam at a sample. The beam gives atoms in the sample a boost of energy. The sample then emits its own X-rays, which can be used to figure out the sample’s elemental makeup. With XRF, scientists have scrutinized fossils. Art restorers used it to find hidden paintings.

Here, the team zoomed in on the ink. Both writers used ink made from iron sulfate. But the same type of ink will contain different amounts of certain elements depending on who made the ink, Michelin explains. She works in France at the National Museum of Natural History in Paris.

Shooting X-rays at the letters turned up differences in the ratios of copper and zinc in the original and censoring inks. Mapping the differences revealed the hidden words, including “beloved,” “tender friend” and “madly.”

The censor, it turns out, was von Fersen himself. The count was known to make copies of the queen’s letters. The ink used to censor the original letters matched the ink he had used to make copies, Michelin says. How much of their relationship was personal versus political may never be known, she adds. But we do know that “he kept these letters, even though it was risky for him.”

Carolyn Gramling is the earth & climate writer at Science News. She has bachelor’s degrees in geology and European history and a Ph.D. in marine geochemistry from MIT and the Woods Hole Oceanographic Institution.

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