The Vatican is renowned for its dedication to traditions, no matter how quirky they may seem. Case and point; the Vatican’s walls.

Architectural Digest reports that the Vatican still uses milk to repaint the exterior of the Belvedere Palace as a part of a technique that has been embraced since 1484. Since the building’s creation, staff have coated the walls with a milk concoction that sees the dairy product mixed with slaked lime. The solution is then hand-patted on to the wall in the belief that the building will age better than a slick of modern paint.

Of course, this being the Vatican, it’s not just any old milk that’s used. But rather the milk is produced by cows that are raised at the papal summer residence near Rome before being transported to the Vatican and applied by one of the 100 full-time cleaning staff.

The choice to paint with milk isn’t one of the only unconventional cleaning techniques embraced by the Vatican. The residence also chooses to clean the near 600 marble statues that sit in and around its gardens with a mixture of essential oils including lavender, oregano, and thyme.