A new3D-printing technique could render a three-dimensional object in minutes instead of hours—at up to 100 timescurrent speeds. The experimental approach uses a vat of resin and some clever tricks with UV and blue LED lights (no lasers needed) to accelerate the printing process. The techniquelooks almost like a time-reverse film loop of an object dissolvingin a reservoir of acid. But instead of acid, thisreservoir contains a specially-designed resin that hardens when exposed to a particular shade of blue light. Crucially, that hardening (the technical term ispolymerization) does not take place in the presence of a certain wavelength of UV light. The resin is also particularly absorbent at the wavelengths of both the blue and UV light. So the intensity of UV or blue light going in translates directly to the depth to which light will penetrate into the resin bath. The brighter the light beam, the further it penetrates and the further its effects (whether inhibiting polymerization in the case of UV light, or causing it in the case of blue light) will be felt in the bath along that particular light path. Timothy Scott, associate professor of chemical engineering at the University of Michigan, says the way to get a 3D-printed object out of this process is to send UV light through a glass-bottomedbasin of resin. Then, at the same time, through that same glass window, send patterns of bright and dim blue light.