The vast majority of 3D-printed objects are plastic. Most FFF (Fused-Filament Fabrication) 3D printers use thermoplastic filament and LCD/SLA (Stereolithography) 3D printers use photopolymer resin. Other materials, like ceramic, concrete, and metal, are somewhat common. We've even seen organic tissue and various foods being 3D-printed on occasion. But glass is difficult to print, because of the temperatures required and the physical properties of molten glass. That's why it is impressive that Lios Design, a team formed by MIT students, is well on its way to perfecting molten glass 3D printing.
Lios Design built its first molten glass 3D printer, dubbed "Version Zero," back in 2014 while the team members were taking a 3D printing course at MIT. The team claims that that was the world's first molten glass 3D printer. Since then, Lios Design has been hard at work on improving the technology. The original Version Zero 3D printer was functional, but the prints were rough — similar to what you'd see from a conventional 3D printer that was very poorly tuned. That was due to difficulties in overcoming the practical realities of working with molten glass. The biggest challenges were thermal management and the viscosity of the liquefied glass.
Newer versions of their molten glass 3D printers are much better. A kiln melts down glass and then the molten glass gets transferred to a special reservoir. The molten glass then gets mechanically pumped through the extruder. The layers are far thicker than on a typical 3D printer, because the molten glass is too viscous to pump through a small nozzle. But the extrusion is very consistent on the newer designs, which allows for some very clean prints — even if the layers are clearly visible.
In order for the layers to adhere well to each other, the extruded glass has to be kept at a high temperature. To achieve that, the printer has an enclosure with a heater. The temperatures required would damage most plastics, so they constructed the printer primarily from metal parts. They have printed numerous artistic objects, like vases and lamps, to demonstrate how well the printer works. Those are stunning to look at and they have even been shown in art galleries. The current version of the printer, Glass II, prints at an architectural scale and is capable of print large objects, as proven by the Morph Table.