Crystal gazing: A simple Pd-catalyzed site-specific nanoetching method was developed to visualize the polycrystalline nature of Fe(3)O(4) (see picture), Fe(2)O(3), MnFe(2)O(4), CoFe(2)O(4), and MnO nanoparticle systems. The technique relies on the very fast etching speed of the grain interface within bi- or polycrystalline nanocrystals.