Now anything can have a fingerprint

THE rising price of metals over recent years, fuelled by booming demand in China and other emerging economies, has caused thieves to turn their attention to things that would previously not have merited a second glance: rubbish bins, manhole covers, traffic lights, industrial piping and—perhaps most worrying—electrical cables, telephone lines and the wires that control railway signals. In one English county alone, the West Midlands, 52 thefts of metal from railways over the course of 18 months have resulted in the delay or cancellation of 1,500 trains, according to Tom Watson, a local member of Parliament. Indeed, Paul Crowther, deputy chief constable of the British Transport Police, the force responsible for keeping an eye on the railways, describes metal theft as the second-greatest threat, after terrorism, to Britain's infrastructure.

It would be useful, then, for scrap dealers who are offered metal objects of unknown provenance to be able to tell quickly whether they have been stolen and, if so, from whom, so that they can inform the police. Two small British firms, SmartWater Technology, based in Telford, and Selectamark Security Systems of Locksbottom, think they have worked out ways of letting them do just that.

SmartWater's invention is a special adhesive that can be painted onto objects that might be stolen. Though invisible in normal light once it has hardened, this adhesive glows yellow when illuminated by a beam of ultraviolet light. That, by itself, acts as a warning that goods might be stolen, but the real trick is what happens next. The adhesive also contains celluloid microdots the size of sand grains that have been imprinted with SmartWater's phone number and a code identifying the metal's owner. These can be read under a microscope and a quick phone call will reveal whether the goods are, indeed, stolen—or have been sold legitimately by an owner who has forgotten to clean them first.

Of course, a thief who believes his swag might have been so marked might attempt such cleaning himself. Thieves sometimes burn off the insulation on electrical cabling anyway. So SmartWater has found a further way to encode information in its adhesives—one which, unlike celluloid, survives fire. Besides the microdots, each batch also contains a unique combination of up to 30 compounds of rare-earth metals. Checking these is a bit more complicated than looking down a microscope. But if a dealer or the police have reason to suspect a piece of scrap might be stolen, then SmartWater's laboratory can tell them who bought the batch of adhesive in question.

Selectamark's technology also uses microdots, though instead of celluloid it employs polyester or a nickel-based alloy, depending on the type of adhesive involved. In place of mixtures of rare-earth compounds, its unique chemical markers are short stretches of DNA, each with a different sequence of genetic code.

DNA, indeed, seems to have a talismanic quality in the fight against crime. Even SmartWater, which does not actually use DNA, refers to its unique chemical identifiers as “synthetic DNA”. Both companies say the mere act of alluding to their products as a type of DNA helps deter criminals—rather as the original DNA-identification technology was often referred to as “fingerprinting”, even though it has nothing to do with fingerprints. Films and television shows have dramatised the use of DNA from crime scenes to convict miscreants, generating what Jason Brown, Selectamark's head of sales, calls a “DNA fear factor”. The police concur, saying that when DNA warning signs are posted prominently, crime drops.

For those not deterred by magic words, though, both firms have an extra surprise. They also sell spray-can kits, to be installed above doors or near valuables. These are triggered by motion detectors or the press of a button by a shop assistant or householder. Even if a thief notices the mist, he is marked for days. The spray lodges in pores and creases in the skin, available to the swab of a curious police officer and branding the thief as effectively as his own DNA would, had he left any at the scene of the crime.