An early medieval writer Theophilus Presbyter, believed to be the Benedictine monk and metalworker Roger of Helmarshausen, wrote a treatise in the early-to-mid-12th century that includes original work and copied information from other sources, such as the Mappae clavicula and Eraclius, De dolorous et artibus Romanorum. It provides step-by-step procedures for making various articles, some by lost-wax casting: "The Copper Wind Chest and Its Conductor" (Chapter 84); "Tin Cruets" (Chapter 88), and "Casting Bells" (Chapter 85), which call for using "tallow" instead of wax; and "The Cast Censer". In Chapters 86 and 87 Theophilus details how to divide the wax into differing ratios before moulding and casting to achieve accurately tuned small musical bells. The 16th-century Florentine sculptor Benvenuto Cellini may have used Theophilus writings when he cast his bronze Perseus with the Head of Medusa'.