Yesterday, Makerbot announced three filament types that will let users 3-D print with materials comprised partially of wood, limestone, iron, or bronze. It's certainly interesting from an enthusiast's point of view, even if it has limitations: you can't mix-and-match different kinds of filaments in a single 3-D printing job, for example. But it's also important to note what this is, and also what it isn't.
The way 3-D printers like the Makerbot work is by heating up a coil of PLA plastic—an eco-friendly plastic dervived from renewable resources—and depositing it, dollop by dollop, on a printing bed, which then hardens. Overtime, this builds up a three-dimensional structure. It works well, but right now, it's impossible to 3-D print things like real wood, limestone, iron or bronze: either the materials can't be melted down at all (wood and limestone), or they can't be melted down at a low enough temperature to be safe for home use (iron and bronze).
So how is Makerbot doing it? The same basic way MIT's Self-Assembly Lab was 3-D printing "wood" back when I visited them last October: by taking sawdust and infusing it through the filament. Basically, it's plastic with tiny piece of wood in it.
This goes further towards mimicking low-quality "real" wood than you might think. When I visited the Self-Assembly Lab, MIT researcher Skylar Tibbits said the composite material could actually be sanded down and stained, much like real wood. But it's also never going to be as high-quality, or as strong, as real wood: it's basically the equivalent of fiberboard, or any other type of engineered wood. And that's likely going to go for limestone, iron, and bronze too. These filaments may look and feel like stone and metal, but secretly, it's all just plastic.
Makerbot's move has some interesting implications for designers, who will now, at the very least, be able to mock-up more realistic looking models of the wood, stone, and metal projects they're working on. But still, don't expect Makerbot's announcement to get us any closer to a 3-D printed Eames chair, or a 3-D printed La Creuset.