How an oddly attributed $19,000 picture proved to be a $100 million work by Leonardo da Vinci--a true art-world detective story In late 2010, art collector Peter Silverman revealed that a "German, early 19th century" portrait he had bought for $19,000 was, in fact, a previously unknown drawing by Leonardo da Vinci--an exquisite depiction of Bianca Sforza, rendered 500 years ago. In Leonardo's Lost Princess, Silverman gives a riveting...