2D macro-XRF to reveal redacted sections of French queen Marie-Antoinette secret correspondence with Swedish count Axel von Fersen.

During the French Revolution, Marie-Antoinette, queen of France and wife of Louis XVI, maintained a highly secret correspondence with the Swedish count Axel von Fersen, her close friend and rumored lover. An unidentified censor later redacted certain sections of the exchanged letters. This presumably sensitive content has been puzzling historians for almost 150 years. We report on the methodology that successfully unraveled this historical mystery. X-ray fluorescence spectroscopy was used in macroscanning mode on the redacted sections. Specific data processing was applied to improve the legibility of the hidden writings (elemental ratios, statistical data reduction, multimodal images fusion, unmixing procedure, and image treatments). This methodology successfully revealed the redacted contents of eight letters, shedding new light not only on Marie-Antoinette and Fersen relationship but also on the author of the redactions. It will also be of great interest for other historical and forensic cases involving the disentanglement of superimposed multi-elemental materials.