The unsigned painting of a woman wearing an outfit with a plunging neckline has been a favorite at the Spencer Museum of Art on the University of Kansas campus for decades. “Over the years, it’s been attributed to a few different artists — first, William Hoare, and then, sometime before the 1980s, to Highmore. But museum curators had never been 100 percent sure of the 1720s-era painting’s true origin, until now.”