The production of a museum-quality, scale replica is a particularly complex task as it is impossible to use moulds taken directly from the original since they’ve been damaged by time. It is only thanks to the combination of the latest 3D technology and lost-wax casting that it was possible to faithfully reproduce the panels to replace the original Doors.
The innovative approach of the “Guild of the Dome” project also lies in its use of traditional techniques of the highest level in the world alongside cutting-edge technology, implementing a process that, for the first time in history, enables a replica of a bronze sculpture of the same dimensions and with the same detail as the original to be obtained.
The “lost-wax casting” technique is a process that dates back to antiquity, which is also used today by the craftsmen of the foundry Fonderia Frilli to reproduce Ghiberti’s bronze panels. It involves the use of a wax mould made by the finest techniques currently available.
The impossibility of creating a mould from the original was overcome by using 3D technology that digitally and in a non-invasive manner generates a model that is even more accurate than the one created manually.
A 3D scan is made of the original panels, which once processed and analysed by experts leads to a prototype from which a silicon negative mould is produced. At this stage, the extraordinary dexterity of the goldsmiths is brought into play, who with specific precision instruments pour high density wax to make the positive model, which is again worked by hand so that none of the details are lost at the time of casting.
After having painstakingly compared the 3D scans with at least 400 photos taken on site of the original work and obtained the approval of the Opera del Duomo and the Ministry of Cultural Affairs, the goldsmiths cover the mould again with a special refractory material and add sprues designed especially for the purpose so that the bronze can be poured as uniformly and precisely as possible. This stage requires three weeks of work and a team of several artisans, each specialized in one particular detail (landscapes, clothing, body parts, etc.).
At this point the wax is melted to make way for the molten cast bronze, which once cooled is separated from the cast and cleaned by ultrasound technology to remove even the smallest residues of refractory material. The last stage involves manual chasing, which brings the panel replica to museum standard.