The 12th century bronze doors of Bonanno di Pisa in Monreale and Pisa: Materials and manufacture

Bonanno di Pisa is, next to Barisano di Trani and Oderisius of Benevento, amongst the most renowned mediaeval Italian bronze casters. Bonanno is responsible for the biggest mediaeval metal door, the almost 8 m high main door of the Cathedral of Monreale, Sicily, built in 1185/1186, and the San Ranieri door of the Cathedral of Pisa, Tuscany, finished in 1180. He was also responsible for the Porta Reale (also Cathedral of Pisa; 1179/1180), which was destroyed in the 1595 fire. Contemporary doors made of bronze or brass are rare: from the 12th century, only about 17 doors are still preserved, nevertheless being part of the biggest complex of mediaeval monumental bronzes. In this paper, the chemical composition as well as manufacturing and assembling of the two preserved doors are discussed. Both the Pisa and Monreale doors were made of leaded tin bronze. In the case of Monreale, chemical analysis confirmed the art historical suspicion that the central leaf was not from Bonanno's workshop, as indicated by a different style and chemical composition. We also identified the types of wood used for the wooden elements of the doors, mainly silver fir (Monreale) and elm (Pisa).