Researchers from ETH Zürich have developed a technique to produce complex glass objects with 3D printing. The method is based on stereolithography, one of the first 3D-printing techniques developed during the 1980s. The researchers developed a special resin containing a plastic and organic molecules to which glass precursors are bonded. The resin can be processed using commercially available digital light processing technology, which irradiates the resin with UV light patterns. Wherever the light strikes the resin, it hardens because the light-sensitive components of the polymer resin cross-link at the exposed points. The plastic monomers combine to form a labyrinth-like structure, creating the polymer. The ceramic-bearing molecules fill the interstices of this labyrinth. Various glass objects created with a 3D printer. Courtesy of ETH Zürich/Complex Materials group. The process allows objects to be built up layer by layer, with parameters that can be changed on a layer-by-layer basis, including pore size: Weak light intensity results in large pores, and intense illumination produces smaller pores. “We discovered that by accident, but we can use this to directly influence the pore size of the printed object,” said Kunal Masania of the Complex Materials group at ETH Zürich. The researchers are also able to modify the microstructure, layer by layer, by mixing silica with borate or phosphate and adding it to the resin. Complex objects can be made from different types of glass or even combined in the same object using the technique. The researchers then fire the blank produced in this way at two different temperatures: at 600 °C to burn off the polymer framework and then at around 1000 °C to densify the ceramic structure into glass. During the firing process, the objects shrink significantly but become transparent and hard like window glass. The 3D-printed glass objects are still no bigger than a die, and large glass objects such as bottles, drinking glasses, or window panes cannot be produced this way — which was not actually the goal of the project, Masania said. Rather, the aim was to prove the feasibility of producing glass objects of complex geometry using a 3D-printing process. The researchers have applied for a patent and are reportedly in negotiations with a Swiss glass dealer who wishes to use the technology. The research was published in Nature Materials (www.doi.org/10.1038/s41563-019-0525-y).