“Painting can never show her nose in company with architecture but to have it snubbed,” said the great English painter, J. M. W. Turner. The 30,000 works on paper that were part of the “Turner Bequest”—donated to the Tate after the artist’s death—were created for his “own pleasure,” according to the critic John Ruskin. That said, the role of watercolors in Turner’s process was critical, because the medium opened up expressive possibilities. Gathered here are 97 watercolors that span the artist’s career and embody his evolving style. —E.C.