We study a crystallographic etching process of graphene nanostructures, where zigzag edges can be prepared selectively. The process involves heating exfoliated single-layer graphene samples with a predefined pattern of antidot arrays in an argon atmosphere at 820 degrees C, which selectively removes carbon atoms located on armchair sites. Atomic force microscopy and scanning electron microscopy cannot resolve the structure on the atomic scale. However, weak localization and Raman measurements, which both probe intervalley scattering at armchair edges, indicate that zigzag regions are enhanced compared to samples prepared with oxygen based reactive ion etching only. (C) 2013 AIP Publishing LLC.