Kircher compares markings in a stone with the edges of a crystal.

When nature takes up a painter's brush

Athanasius Kircher (1602–1680), a German Jesuit scholar working in Rome, devoted a richly illustrated book to the world underground. In his treatment of stones he leads his reader from the regular shapes of crystals to coloured designs in rock. The transition is brief enough to pass almost unnoticed. Yet Kircher treats the change as if it were a move from one workshop to another. Nature, who a moment ago was busy as a geometer, now exercises the abilities of a painter.

From an edge to a picture plane

First, in stones she performed all the tasks of a good geometer. […]

– Athanasius Kircher, Mundus subterraneus, 1678, p. 22.[1]

Someone examining a crystal point is likely to notice its edges, its planes and their relations. What one can recognise in a stone takes on a different sense when the object has a pattern of coloured veins. Lines may branch like twigs. A change from dark to light may call to mind a distant landscape. To perceive such similarities the viewer has to bring experience from somewhere else. Kircher places this activity of the eye close to the experience of looking at a picture.

Whose work appears in the stone?

His decision to attribute both arts to the same agent matters. There is a continuity between a crystal's order and the surprise of finding an apparent scene in figured stone. The reader has to alter the way they look. The change of tools in Kircher's metaphor makes this particularly clear. Compass and brush prompt different questions about the same surface. The material can sustain both kinds of attention without a human hand having to add a single line.