A method is provided for producing an article which is transparent to infrared radiation. The method includes the steps of (a) disposing a population of nanoparticles on a substrate, wherein the population of spherical nanoparticles has a population variance of less than 10% in at least one parameter selected from the group consisting of diameter and maximum dimension; (b) subjecting the nanoparticles to spark plasma sintering, thereby producing a sintered product; and (c) removing the sintered product from the substrate as a self-supporting mass.