Feb 032011
Adhesives,Polyvinylalcohol adhesives,PVAL

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Special transparent adhesives, dabbed on valuables or sprayed on thieves, are helping police solve crimes

THE rise in the 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 of the sort often used in discotheques.

That, by itself, acts as a warning that goods might be stolen, but the real trick is what happens next. For 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, it is open to a thief who believes his swag might have been so marked to attempt such cleaning himself. Also, thieves sometimes burn off the insulation on electrical cabling anyway. So SmartWater has found an additional 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 just looking down a microscope. But if a dealer or the police have reason to suspect a piece of scrap might have been stolen, then a trip to SmartWater’s laboratory will be able to tell them who bought the batch of adhesive in question.

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