It seems like there’s always something new to discover in the thousands of pages of notes and drawings left behind by Leonardo da Vinci, whether it’s a sketch for an early refrigerator or an illustration of a viola organista fusing a piano with a stringed instrument. Recently at the British Library (BL) in London, multispectral imaging revealed a nude male figure that was erased five centuries ago.

The hidden sketch is part of the Codex Arundel, a collection of Leonardo’s papers named for its former owner, collector Thomas Howard, 14th Earl of Arundel. Erin Blakemore at Smithsonian.com notes that multispectral imaging is “gaining steam among conservators who want to get a better look at historical objects without damaging them,” since it’s non-invasive, combining multiple images of an object taken at different wavelengths. The same technology recently revealed over 60 tattoos on the mummy of Ötzi the Iceman, a lost portrait beneath a 1901 Picasso painting, and the hidden geographic details of the 1491 Henricus Martellus world map.

Imaging scientist Dr. Christina Duffy explains more about the process used on the Leonardo codex at the BL Collection Care blog:

The analysis took place at the British Library Centre for Conservation where high resolution images of the folios and region of interest were captured. Multispectral imaging is one of the many tools our Conservation Science team use to non-invasively and non-destructively increase the body of knowledge on collection items for scholars, curators and conservators. The da Vinci sketch was placed underneath the monochrome sensor camera and exposed to light of various wavelengths ranging from the ultraviolet at 365 nm to the near infrared at 1050 nm. … The images raise fascinating questions about why the figure was drawn here, and why great efforts were made to erase it.

The BL has refrained from speculation and conspiracy theories, as it’s not clear whether Leonardo himself erased the man, but that hasn’t stopped others. Martin Kemp, Oxford University emeritus professor of art history, told the Sunday Times that the figure looks like Michelangelo’s “David” and posited that Leonardo may have erased it “because he did not want people to think he was full of adulation for Michelangelo.”

The page with the lost figure is on view through the end of March in Treasures of the British Library. If you want to take a closer look and conjecture for yourself — perhaps it’s a secret lover? a Knights Templar code? an underdog Mona Lisa subject? — the Codex Arundel is also available for viewing online, and there are images of the different layers of multispectral imaging on the BL Collection Care blog.

h/t Smithsonian.com