Over its 90 years of existence, the Museum of Modern Art (MoMA) in New York has acquired an astonishing collection, with more than 3,500 paintings and sculptures, 11,000 works on paper, and 60,000 prints and multiples. But its holdings go much deeper. “We estimate we have something like 6.5 million items,” the museum’s Chief of Archives, Library, and Research Collections, Michelle Elligott, says of her department’s files. “That’s not a very precise estimate, because I have not gone in to count every single one of them, but it gives you…