Ink analysis reveals Marie Antoinette’s letters’ hidden words and who censored them

By | October 1, 2021

In a world torn apart by the French Revolution, doomed Queen Marie Antoinette exchanged secret letters with a rumored lover. Someone later censored them — and now scientists know who.

Chemical analyses of the ink reveal not only the obscured words, but also the identity of the censor, researchers report October 1 in Science Advances.

From June 1791 to August 1792, as Marie Antoinette and the rest of the royal family were confined to Paris’ Tuileries Palace following an escape attempt, the queen managed a clandestine correspondence with Swedish Count Axel von Fersen.

Whether the correspondents exchanged words of love or state secrets was a longstanding mystery, says Anne Michelin, a chemist at the National Museum of Natural History in Paris. Michelin and colleagues unraveled this mystery using X-ray fluorescence spectroscopy.

XRF, a noninvasive technique, works by shooting an X-ray beam at a sample, kicking the atoms in the sample into a higher-energy state. The sample then emits its own X-rays along a spectrum characteristic of its elemental makeup. With XRF, paleontologists have scrutinized fossils and art restorers have found hidden paintings (SN: 5/10/10; SN: 8/4/16).

An X-ray fluorescence scanner analyzes the ink in a letter dated September 26, 1791, written by the French Queen Marie Antoinette to the Swedish Count Axel von Fersen.@CRC

Here, the researchers zoomed in on the ink. Both correspondents used common gall ink made from iron sulfate, but different inks contain different proportions of trace elements, depending on the source, Michelin says. The team scanned the letters pixel by pixel, finding consistent differences in the copper-to-iron and the zinc-to-iron ratios of the original and redacting inks. By mapping each pixel’s elemental differences onto a gray scale, the hidden words emerged — words such as “beloved,” “tender friend” and “madly.”

As for the censor, it was von Fersen himself, Michelin says. The count was known to make copies of Marie Antoinette’s letters — and the ink used for the redactions was a match to those copies.

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.”