A question that arises frequently among those who come in contact with the Duomo di Milano and its restoration sites for the first time regards the substitution of the Cathedral's statues and damaged parts: "When do you decide to replace a sculpture?", "According to what criteria is the state of the marble evaluated?", "Are they substituted with copies?" and what techniques are used?
Ever since the first signs of wear became evident, starting in the 17th century, the substitution of the most damaged parts of the Duomo has been a constant practice for the Veneranda Fabbrica. This means that just two centuries after construction of the marble cathedral was initiated, restorations began taking place contemporaneously with the edification of the monument, a symbol of the city itself.
"Substitution" may seem like a brutal measure, masked by a modest nonchalance for remaking, but in reality it has nothing to do with replacing what history has bequeathed us. It is of utmost importance to preserve against wear that which history has left behind, precisely because this is part of a process in which our lives are rooted and its results must not be stilted: Unlike many other vestry boards, the Veneranda Fabbrica has, for the past 630 years, maintained its objective, mission, and function for this very reason.
The maintenance of this architectural structure is the responsibility that the Fabbrica has undertaken, a commitment to the people of Milan and to the world, as the custodian of a cultural heritage that belongs to all of humanity. This entails a constant succession of restorations necessary for the preservation of the monument's integrity and to guarantee the safety that would be jeopardised by potential falls, for example of elements from the perimeter walls.
In the 19th century the formation of an international consciousness regarding architectural restoration led to an enormous increase in the number of projects: the completion of parts missing from the tiburium and from the façade, the construction of new spires, and, at the same time, recorded in 1885-86, the replacement of the first statue in a serious state of disrepair. Following this first episode, thanks to the report by Arch. Paolo Cesa Bianchi, a new chapter in the Fabbrica's duties was begun: "Substitutions".
But what does it mean to make a copy? What technique is used?
From the classical era to the Roman era, various sculptural practices have existed for the reproduction of the marble mantle which, over time, have been honed and developed. To name a few: the use of 3 compasses, the plumb line with grid, compass and graduated set square, and "appuntatura" or pointing .
The pointing technique consists in the moving of a T-shaped frame made up of two wooden slats, on which 3 pointed pins are affixed at the three extremities. The 3 pins become the support for holding the frame 15-20 centimetres up from the surface of the model and therefore of the marble to be sculpted. These rest on 3 small holes first dug into the model and then into the pre-shaped marble, thus becoming the lead points, the same ones that will support the frame each time it is moved.
The T-shaped frame used today is constructed from 2 brass tubes, similar to the wooden ones, with hinged arms that, at their extremities, have an approximately 30-cm long sliding needle which is used to determine the height of the points. The many points thus measured on the model, through a procedure that is repeated many times, guarantee the fidelity and extreme accuracy of the copy.
The advantage of pointing, as compared to other techniques, is in the certainty of the material removed and in the absolute precision of the relationship between the points.
In the words of Nicola Gagliardi, a sculptor for the Veneranda Fabbrica del Duomo di Milano for over 30 years: "it is an indispensable technique that makes it possible to recover the historical accuracy of original sculptures".