They mapped this to reveal the original text. In a subset of eight letters, they found consistent differences in the copper-to-iron and zinc-to-iron ratios of inks in the original texts and ink in the redactions. To unravel the mystery of this content, the researchers applied X-ray fluorescence spectroscopy вЂ“ a non-destructive chemical analysis вЂ“ to analyse the redacted sections of 15 letters.

Some of the letters Marie-Antoinette exchanged with von Fersen between June 1791 and August 1792 are held at the French national archive.ДЇor almost 150 years, redactions to these texts by an unidentified censor have puzzled historians. They suggest it may have broader historical and forensic applications, demonstrating the power of combining advanced data processing tools with macroscopic elemental mapping to disentangle superimposed ink and to make hidden content more legible. The study also uncovered evidence to suggest von Fersen censored the letters himself, indicating they were important to him either for sentimental or political reasons.ДЄnne Michelin, Centre de Recherche sur la Conservation (CRC), MNHN, Sorbonne-University, CNRS, and colleagues conclude that their strategy offers an alternative to existing methods for unveiling redacted content.

Redacted letter