Three hundred years ago, discriminating travelers in the European countryside might have carried with them an optical instrument called a “Claude glass” after the seventeenth-century French landscape painter Claude Lorrain. A small, tinted mirror, it lent the scenes it reflected a painterly quality evocative of Claude’s idealized landscapes. By the early nineteenth century, a set of colored lenses that could be held to the eye was available to American sophisticates searching for scenery on steamboat trips through the Hudson River Highlands. Voyagers used their filters to sweeten the vistas (