Depicting a bearded man wearing a tunic, the marble statue has adorned one of the Duomo's 135 spires for two centuries.
But decades of harsh weather, pollution and the bombings of the Second World War have taken their toll, leaving it discoloured and missing its right hand.
The damage to the statue was spotted during the twice-yearly inspections of the cathedral, by the institution that has managed the building for 600 years, the Veneranda Fabbrica del Duomo di Milano.
Too fragile to put back, Calderino has created a perfect replica to take its place -- the latest of a steady stream of replacements that maintain the splendour of one of Italy's most famous monuments.
Born from a block
"For me, a statue is like a child that I see grow day by day. It is fascinating to see it born from a block of marble after months of work," Calderino told AFP at the workshop, where around 20 stonemasons practise their craft.
There are more than 3,400 statues on the Duomo, on which construction began in 1386.
They are carved from the dazzling pink-white marble from Candoglia quarry near Lake Maggiore northwest of Milan -- and from where Calderino and his colleagues still take marble today.
"Candoglia marble is very beautiful, very special, but it is difficult to work on because it has very large calcite grains that can break, so it is fragile," said Marco Scolari, the geologist in charge of the workshop and quarry.
The techniques of the team in Milan would also be recognisable to the craftsmen of old, albeit with some technological help.
First, Calderino, 46, makes a rough outline in the marble with his chisel.
Then with surgical precision, he sculpts it with a pneumatic hammer, before smoothing it with an abrasive stone.
'Adopt' a statue
In the small backyard of the workshop, the old statues form a silent crowd, waiting for a new home.
Of the around 100 decapitated, disfigured or limbless figures, several have a small white sign around their necks saying "adopt a statue!"
For an annual fee of 25,000 euros ($26,280) for up to three years, companies can take in one of the Duomo statues -- and in doing so, benefit from a tax break, and a little history.
Consulting firm Deloitte took in an imposing depiction of biblical hero Samson and the lion he is said to have killed with his bare hands, created in the 17th century by Giovanni Battista Buzzi.
Such 'adoptions' "bring a little piece of the Duomo into their company", said Elisa Mantia, the Duomo's culture and conservation coordinator.
Many of them end up in the Duomo Museum, where the statues can be admired close up.
