In the basement of the Biblioteca Ambrosiana, in Milan, a conservator named Vito Milo had just applied a small gel strip to the edge of a 500-year-old drawing in order to dissolve the glue that joined it to a larger paper frame. Now, with a scalpel, he worked loose a few millimeters of the drawing. I asked Milo what was in the gel, and after he rattled off a list of ingredients in Italian, I offered a layman’s rough translation: “special sauce.” He smiled and nodded. “Si, special sauce.”
The drawing was a page from Leonardo da Vinci’s Codez Atlanticus, and I had been invited to witness the painstaking process of its conservation. One morning last winter, I descended to the conservators’ laboratory, which occupies a room just outside the steel-and-glass doorway to the Ambrosiana’s gleaming vault. At the bottom of the stairs, I was stopped by an attendant, who took a coffee cup from my hands and placed it out of harm’s way.