Examples of ice particles produced by syringing water droplets into liquid nitrogen. The polycrystalline nature of the ice is evident from the physical appearance of the particles, as is the anisotropy and roughness of the surfaces. The particles indicated by a solid circle are examples of the sort of particle that was selected for the experiments. Particles such as the ones indicated by a cross were rejected because of their irregular shape and particles such as the ones indicated by a dashed circle were rejected due to their hemispherical shape.