Televisions, car bumpers, computers, telephones. They may be a bit more expensive than your typical soft-drink bottle, but their plastic Is just as recyclable. Until recently though, only the bottles tended to be recycled. With good reason - each bottle is made ot only one type of plastic, which makes them easy to sort and profitable to reuse. The mixture of plastics in more complicated goods poses problems. Consumer-electronic devices, such as telephones, are made up of as many as fifteen different kinds of plastic. A black plastic, say, for the case; a different black plastic for the numbered buttons; a grey plastic for the redial button; and so on. Taking apart and sorting these would be time-consuming enough, even if all that had to be done was to separate by colour. But plastic must be sorted by its chemical composition as well, and this is where the biggest problem lies. Each type of plastic has its own signature. This is its 'absorption spectrum' - a pattern of frequencies of infra-red light, invisible to the eye, that is absorbed when the rest is reflected from its surface. Traditional plastic-sorting devices exploit these signatures to determine what type of plastic something is made of. But black things absorb so much light that conventional sorters cannot distinguish between them. The easiest thing, therefore, is to throw them away.