J.M.W. Turner's lifetime (1775-1851). was also the classic age of the English watercolor, and his mastery and perfection of the medium coincided with its establishment as an independent art form. He rarely left his home without a sketchbook, pencils, and a small traveling case of watercolors. He exploited as no one before him the medium's luminosity and transparency, conjuring light effects on English meadows and Venetian lagoons and gauzy mists over...