The other most-fascinating encounter of the day: A late 19th-century silk-taffeta jacket, meant to be worn with a bustle, with underarm discolorations that suddenly made it feel jarringly real and hauntingly old. “You can’t wash it — it’s there forever,” Mertens mused. He pulled out another dress marred with a dark-colored blotch. “Is that beef stew from 1880?” we wondered aloud. “I think that’s tomato soup, really,” he said. “It’s very sour. And it’s on the lap so I think it must be food.”