What goes around, comes around

GLASSMAKING began 4,500 years ago, in Mesopotamia. The industry’s first products were trinkets, such as beads and pendants, cast from moulds and carved by hand. But craftsmen quickly worked out how to make more practical stuff, such as jugs, bottles and drinking vessels, by coiling strands of molten glass around a sand or clay core of appropriate shape, which could then be shaken or scraped out after the glass had cooled. Since those early days, many other ways of forming glass have been invented. These range from blowing forcefully through a tube to inflate a hot gob of the stuff, creating a hollow vessel, to floating it as a liquid on a bed of molten tin to produce perfectly flat window panes. But ancient wisdom often still has value, and now a group of researchers at the Massachusetts Institute of Technology have had another look at the coiling method, pronounced it good, and modernised it. Their principal updating is to dispense with the core. Instead, they have turned to the field of 3D printing—or additive manufacturing, to give its formal name. Objects of rare beauty, and possibly of great utility, result. Neri Oxman and Peter Houk, the team’s leaders, started with the form of 3D printing most familiar to hobbyists. Fused-deposition modelling, as it is known, works by extruding a filament of semi-molten material (in desktop applications this is usually a thermoplastic) through a mobile nozzle in a pattern controlled by a computer. This builds up whatever object the software is programmed to create. Using glass instead of plastic requires higher temperatures, but the principle is the same. The researchers’ first efforts failed because the filament—pulled by gravity from a hole in the bottom of a crucible heated to 1,000°C—had an irregular diameter. This, and too-rapid (and therefore uneven) cooling to room temperature, led to poor adhesion between successive coils as an object was built up, and also to stress within the filament as it solidified. That meant the finished product was often fragile.