The baptismal font in the Siena Cathedral, crafted by the most important sculptors of the Renaissance, including Donatello, Jacopo della Quercia and Lorenzo Ghiberti, is back in public view after three years of in-depth diagnostic investigations and innovative conservation. The complex work was carried out by specialists from the Opera and the Opificio delle Pietre Dure, the conservation workshop of the cathedral which has been maintaining and restoring elements of the cathedral complex since the 12th century.

The font is made of white marble, gilded bronze and enamelled copper and was created between 1417 and 1431. It has a hexagonal basin with six gilded bronze reliefs depicting scenes from the life of John the Baptist on each of the sides, with gilded bronze statues of the virtues between them. Two of them, Faith and Hope, were made by Donatello. He also created one of the reliefs, The Banquet of Herod. Lorenzo Ghiberti, creator of the breathtaking bronze reliefs in the door of the Baptistery of Florence, made the The Baptism of Jesus panel, and the dynamic Arrest of John the Baptist.

The bronzes were gilded with an amalgam of gold and mercury, a process known as fire gilding. It is highly susceptible to tarnishing and abrasion. The OPD conservation team removed the bronze panels and sculptures from the basin to restore them in the laboratory. The marble elements were restored in situ and a new support structure for the stone elements was designed to give access to the back of the bronzes in the future without having to dismantle them.

Out of the white marble basin rises a monumental tabernacle, also made of white marble, crowned by a slender lantern topped with a sculpture of John the Baptist. It was designed in the style of a classical temple with a segmented dome. It is adorned with marble sculptures of five Prophets in niches, one of them by Jacopo della Quercia. The sixth side features a gilded bronze door depicting the Madonna and Child by Giovanni di Turino. Above them were six bronze Spirits. Only four survive today, two by Donatello, two by Giovanni di Turino. The marbles were originally decorated with polychrome blue and gold painted details, much of which has eroded. What is left was revived by the restoration.

Because by its nature the font exposes these priceless artworks to constant moisture that is the opposite of ideal conservation conditions, the OPD will be keeping a close eye on the font, with constant environmental monitoring, a new humidity control system and a thorough inspections every six months. That will allow conservators to detect any signs of deterioration immediately and take countermeasures before damage sets in.