3D printing with paper: Print me the head of Alfredo Garcia THERE are more than a dozen sorts of three-dimensional (3D) printer. They all build up objects, layer by layer, but what the layers are made of varies from one to another. Some extrude filaments of molten plastic. Some spray special "inks," such as liquid polymers that solidify when exposed to ultraviolet light. Some use powdered plastic or powdered metal that is then fixed in place with a laser or an electron beam. Now there is yet another way. Staples, an office-supplies company, has introduced it at its store in Almere in the Netherlands. And the layers their machine prints are made of a substance that Staples has in abundance: A4 sheets of paper. The process was invented by Conor MacCormack, an Irish aerospace engineer, and his brother Fintan, an electrical engineer. They worked with 3D printers but found the materials expensive. Many manufacturers put a high markup on their bespoke printing materials, just as the producers of 2D printers do on their ink. The MacCormacks therefore set out to make a full-colour 3D printer with exceptionally low operating costs. They call the result "Selective Deposition Lamination" (SDL) and they reckon the cost of the paper needed for it works out at about 5% of the cost of the materials for other 3D systems. Like those other systems, SDL begins by taking a series of digital slices through the object to be replicated. These are then sent to the printer, which reproduces each layer in turn. In the case of SDL, the process starts by the machine applying drops of adhesive to a sheet of paper. More adhesive is applied to the area which will form the first layer of the object; less (but still some) is applied elsewhere. The lightly glued area acts as a support while the structure is built up. Next, the machine slides a second sheet of paper on top of the first and presses them together to bond them. This done, it uses a tungsten-carbide blade to slice around the outline of the object (ie, between the heavily and lightly glued areas). The process continues, layer by layer, until the object is complete. It is then removed from the machine, the supporting material is peeled away, and the finished item, which has a consistency similar to wood (not surprising, since paper is made of wood pulp), is revealed. Adding colour involves a bit of old-fashioned two-dimensional printing. Each sheet, before it is put in the stack, is printed top and bottom with appropriate ink in a pattern that follows the edge of the item at the level this sheet of paper will occupy. The ink soaks through the paper so that when it is cut no white is visible. So far the new printers, which are made by the MacCormacks" company, Mcor Technologies, have been used mainly to produce things like architects" models, three-dimensional maps, prototypes of parts, moulds and various arts-and-crafts items such as figurines. A doctor is also using a Mcor machine to make surgical guides for facial reconstruction. Staples hopes people will use their imaginations and print all sorts of other things as they expand the service to more stores. And one day, as more office documents migrate to cyberspace, 3D printing with paper may even overtake the 2D sort.