Eugene Delacroix's most famous painting, "Liberty Leading the People," hangs in a revered spot in Paris' Louvre Museum. Inspired by the 1830 Paris Uprising, it has been held up as an embodiment of the French national ethos, and most recently as a justification for the country's controversial burkini ban.

But "Liberty Leading the People" may also have been literally painted with people.

From at least the 16th century until as late as the early 1900s, a pigment made from mummified human remains appeared on the palettes of European artists, including Delacroix. Painters prized "mummy brown" for its rich, transparent shade. As a result, an unknown number of ancient Egyptians are spending their afterlife on art canvases, unwittingly admired in museum galleries around the world.

Mummies for Medicine and Entertainment

The use of mummy as a pigment most likely stemmed from an even more unusual use—as medicine. From the early medieval period, Europeans were ingesting and applying preparations of mummy to cure everything from epilepsy to stomach ailments. It's unclear whether Egyptian mummies were prized for the mistaken belief that they contained bitumen (the Arabic word for the sticky organic substance, which was also believed to have medicinal value, is mumiya), or whether Europeans believed that the preserved remains contained otherworldly powers.

What is clear to researchers is that early artist pigments were derived from medicines at the time, and were commonly sold alongside them in European apothecaries. And just as mummy was waning in popularity as a medical treatment, Napoleon's invasion of Egypt at the end of the 18th century unleashed a new wave of Egyptomania across the Continent.

Tourists brought entire mummies home to display in their living rooms, and mummy unwrapping parties became popular. Despite prohibitions against their removal, boatloads of mummies—both human and animal—were brought over from Egypt to serve as fuel for steam engines and fertilizer for crops, and as art supplies.

View Images A 1937 view of the British Museum's mummy room. It's possible that mummy remains may also be present in the museum's painting galleries. Photograph by Fox Photos, Getty Images

By the beginning of the 20th century, however, the supply of quality mummies for pigment appears to have dried up. A 1904 ad in the Daily Mail requests one "at a suitable price," adding: "Surely a 2,000-year-old mummy of an Egyptian monarch may be used for adorning a noble fresco in Westminster Hall…without giving offence to the ghost of the departed gentlemen or his descendants."

Did Artists Know Whom They Were Painting With?

Nonetheless, many artists may have been unaware that mummy brown was a pigment actually made from mummies. "You just wouldn't expect that to happen," says Gary Bowles, a representative of C Roberson and Co. In the 19th and early 20th centuries, Roberson was one of Europe's preeminent "colorists," supplying paints and pigments to everyone from the artists of the UK's Royal Gallery to amateurs like Winston Churchill.

Until 1933, Roberson's featured mummy brown in their artist's catalog, and Bowles recalls seeing mummy parts in the shop as late as the 1980s, when the company was bought out. "There's no more mummy brown around," he confirms.

In one unusual anecdote about the pigment, the writer Rudyard Kipling describes a day in the 1860s spent with two pre-Raphaelite painters, Edward Burne Jones, Kipling's uncle, and Lawrence Alma Tadema. After Alma Tadema informed his colleague that mummy brown was indeed made from mummies, a horrified Burne Jones retrieved his tube of mummy from his studio and buried it in the yard. "[H]e descended in broad daylight with a tube of 'Mummy Brown' in his hand, saying that he had discovered it was made of dead Pharaohs and we must bury it accordingly," Kipling recalls.

View Images A drawing of Edward Burne Jones at work. The artist allegedly buried his tube of mummy brown once he was told that it actually contained mummy. Photograph from Bettman Archive, Getty Images

"Alma Tadema was an important customer at Roberson at the time they were grinding up mummies in the mid-nineteenth century," says Sally Woodcock, a painting conservator and researcher at the Roberson Archive of the University of Cambridge's Fitzwilliam Museum. "It's quite possible that he had seen it being prepared."

Woodcock notes that many of the pre-Raphaelite artists who purchased mummy brown from Roberson, such as Alma Tadema, painted Egyptian scenes. "It would be quite interesting to see if these artists were using mummies to paint mummies," she adds.

Why Mummy Brown Will Remain a Mystery

But while we know that mummy brown was a pigment sold by shops and purchased by artists, it's almost impossible to scientifically determine what specific paintings may feature the pigment, even through the use of mass spectrometry.

The few recipes that exist for making mummy brown vary wildly, with some calling for the use of the whole body and others using "only the finest muscle." In addition, the techniques for mummification changed over the centuries, with different resins, oils and plants used at different time, notes Alan Phenix, scientist and head of Treatment Studies research at the Getty Conservation Institute.

"The things that might have been used in embalming and wrapping, such as mastic resin, are all used by artists as varnishes, vehicles, or additives, so to say that something is associated with [mummy brown] is extraordinarily difficult," says Barbara Berrie, head of scientific research at the National Gallery of Art. "The characteristic molecules that would let you know it was of mammalian origin would likely be present in very small quantities."

While the use of embalmed Egyptians as paint pigment has long been out of vogue, art suppliers are still selling tubes of paint called "mummy."