X-ray zone plates are diffractive focusing optics composed of concentric rings of phase-shifting material with a changing period along their radii. Hard x-ray zone plates operate primarily in a range of photon energies from 3 to 30 keV. In order to achieve needed resolution and efficiency, high-aspect-ratio structures are typically patterned and fabricated by gold electroforming into a dielectric mold. Ideally, the molds would be mechanically stable and radiation resistant. Ultrananocrystalline diamond offers a solution with a set of physical properties that suggests that the material can be fabricated to desired requirements. The authors present here the first results for the fabrication of hard x-ray zone plates using an ultrananocrystalline diamond mold for electroforming gold and discuss future developments for creating an optimized focusing optic. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3501357]