In the long history of the Duomo's construction, the word "chiave" comes up repeatedly, a term which indicates a particular kind of metal fitting used to connect and fasten together separate architectural elements.
In this interesting drawing, architect Adolfo Zacchi carefully and expertly illustrates a series of chiavi [anchor bolts] and tie-rods with different shapes and mechanisms, providing the specific name of each element.
In fact, in the 1940s he dedicated himself to a detailed study and survey of all of the anchor-bolts, tie-rods, and ligatures that made up the central nucleus of the Great Spire, in view of a subsequent restoration that would take into consideration not only the separation and fragmentation of the marble, but also the state of preservation and the functionality of the metal fasteners.
In the past, anchor-bolts and tie-rods were made from iron, a material subject to a high degree of alteration and degeneration, especially if exposed to humidity, with obviously damaging consequences to the marble portions.Little by little, over the course of the 20th century, iron was replaced by stainless steel and, in recent years, titanium for the exposed parts.
The Veneranda Fabbrica, always committed to finding the most effective and long-lasting solutions, has also, for the most recent restorations, been able to considerably reduce the quantity of metal parts used in the fittings.
To take a look at and remain up-to-date with the latest restorations taking place at the Duomo di Milano, please visit the Restoration Journal.