The Night Life of the Gods by Thorne Smith

Quirky inventor Hunter Hawk strikes gold when he invents a device that will enable him to turn living matter into stone and to reverse the process at will. After a chaotic field test he meets stunning 900-year-old Megaera who teaches him to turn stone into flesh. The two and a bunch of friends set their sights on New York City to bring the Roman gods of the Metropolitan Museum of Art to life. Among other incidents, Mercury shows himself to be an expert pickpocket, while Neptune causes chaos in the fish market.