Identifying the chemical makeup of pigments used in ancient documents, paintings, and watercolors is critical to restoring and conserving the precious artworks. However, despite numerous efforts, scientists had been unable to determine the source of folium, a popular blue dye used to color manuscripts in Europe during the middle ages — from the 5th to the 15th century. Now, a team of researchers from Portugal has finally uncovered the mysterious ingredient responsible for the gorgeous blueish-purple tint that helped bring ancient illustrations and texts to life.