The Museo del Bargello is home to an extraordinary set of portraits of the Medici family, which have been carved from porphyry, a dauntingly hard stone to work.
The portraits are by Francesco Ferruci del Tadda (1497-1585), a member of a long established family of expert stone workers from Fiesole, who was the first sculptor since the days of classical antiquity to work porphyry on a large scale.
In the 1550s Cosimo I de' Medici (r. 1537-74) embarked on a campaign to make the royal and imperial stone of porphyry the special province of the ruling family of Florence.
The technique of working porphyry, which can only be done with specially tempered steel chisels, is very slow and laborious. A head in relief, for example, would take several months to complete, while a large figure in the round could take as long as a decade.
Tadda would go on to carve the porphyry figure of Justice on the eponymous Colonna della Giustizia, which stands in Piazza Santa Trinita.