I HAVE been much interested in Miss Raisin's Royal Society paper “On certain structures formed in the drying of a fluid with particles in suspension,” of which an account appears in NATURE for June 2.

The expanding ink droplet shears the underlying acrylic paint layer—the Marangoni effect. Saw a shop that was selling these as "fern fossils" when I, for once, looked smart when saying, "Actually...." ...