New conservation research has verified James McNeill Whistler ‘s earliest-known portrait, experts say. The exceptionally rare painting reveals the young artist during a crucial period of experimentation that would propel him to stardom as one of London’s most radical Victorian painters. The pocket-sized painting, produced while Whistler was living in Paris during his early 20s, is included in a monumental survey of the American artist’s life and art at Tate Britain . There, it has been reunited with four more oil portraits from the same period, more than 120 years since they were last exhibited together. One highlight of the group is a previously unseen self-portrait of Whistler smoking from a private collection. For the first time, sketchbooks from Whistler’s teenage years are also being made public, further transforming our understanding of the artist’s early development. “The works just haven’t been shown since Whistler died,” said the show’s curator Carol Jacobi .…