Exhibition note

The show begins with a rock, but what a rock it is. Inside the entryway of “The American Pre-Raphaelites: Radical Realists” at the National Gallery of Art hangs the most famous watercolor painted by the Victorian firebrand and art critic John Ruskin. Fragment of the Alps (ca. 1854–56) depicts a block of gneiss teetering on the edge of a rubble field, set against a cobalt sky. Deep striations in the boulder show the movement of once-molten magma, while veins of feldspar glimmer and seams of iron wash its surface in red and orange. Ruskin was enthralled by the spiritual potential of nature. At a time when the Royal Academy’s students spent their days sketching the muscular bodies of Greek plaster casts, Ruskin instructed his to go outside and draw the first stone they came upon.

Ruskin never traveled to the United...