A new silica nanoparticle-based ink makes it possible to create intricate glass reaction vessels and optical components with a three-dimensional printer (Nature 2017, DOI: 10.1038/nature22061). Although 3-D printing has been growing in popularity, the materials it’s been able to shape have been limited to polymers, ceramics, and metals, says Bastian E. Rapp of Karlsruhe Institute of Technology. Researchers have tried to 3-D print glass in the past, but the high melting temperature of the material has been a challenge. For instance, melting a glass filament in a 3-D printer has resulted in parts with low resolution—on the order of millimeters—and rough surfaces not suitable for use in optics. To overcome these difficulties, Rapp and coworkers adapted a “liquid glass” composite ink made from silica nanoparticles and UV-curable hydroxyethylmethacrylate monomers that they previously developed for making molded glass objects. To make the material compatible with a 3-D printing method called stereolithography, which builds objects layer by layer using UV light to turn monomers into polymers, they removed a solvent from the liquid glass to make it more transparent. The researchers also had to make sure the material could mechanically withstand the printing process. So they made it stiffer by adding higher molecular weight triacrylates. Using the modified ink with a 3-D printer, the researchers created structured objects, heated them once to burn off the polymer and then a second time up to 1,300 °C to sinter the nanoparticles, leaving pure, transparent glass parts with a resolution of tens of micrometers.