The Codex Atlanticus is one of the most extensive and fascinating collections of Leonardo da Vinci's drawings and writings. Its preservation is a great challenge for scholars and researchers. An in-depth study, published in Scientific Reports, was conducted by Politecnico di Milano on folio 843 of the Codex, to understand the origins of some black stains that appeared a few years ago on the modern passepartout that binds Leonardo's original folios.