Whatever Filippo's method of controlling the curvature of the dome, it
had its critics. Not surprisingly, the most insistent of these came from the
camp of Lorenzo Ghiberti. Late in 1425 Lorenzo's deputy, Giovanni da
Prato, appealed to the wardens that Filippo was failing to observe the
terms of the 1367 model. As capomaestro, Filippo had of course sworn his
allegiance to this sacred structure, just like all of the capomaestri before him.
Yet Giovanni was dissatisfied. Fe voiced a number of complaints, the
most serious of which was a claim that Filippo was not building the
cupola according to the proper profile, the quinto acuto or 'pointed fifth'
curvature established by Neri di Fioravanti.