The Renaissance sculptures in Florence’s Piazza della Signoria, including the replica of Michelangelo’s David, will soon have a shiny new neighbor: Jeff Koons’s Pluto and Proserpina (2010-13). The 11ft work in gold-colored stainless steel will stand in front of the Palazzo Vecchio, Florence’s town hall and civic museum, from September 25 until December 28. Inside, Koons’s Gazing Ball (Barberini Faun) (2013), from his series of plaster casts of Greco-Roman sculptures, will be presented in the Hall of Lilies, where Donatello’s original bronze Judith and Holofernes (around 1457-64) is on permanent display.