Once the University of Leicester scientists knew that fingerprints could corrode metal, they applied a very large electrical charge--2,500 volts--to the corroded area. They then applied to the metal a very fine, black conducting powder similar to photocopier toner, which adhered to the areas of corrosion. "You could see the outline of the fingerprint in the black powder, thereby rendering the fingerprint visible," says Bond.

Johnson thinks that the technique is exciting but warns that the surface area of cartridges is so small that the entire print may not be obtained. "One of the major issues in fingerprint analysis is how much of the print is necessary before you can reliably say it is someone's fingerprint," says Singer. In general, though, Singer is impressed with Bond's research. "The more methods we have to develop invisible fingerprints, the better off we are."

Bond says that the technique has been extensively tested in the lab and will be applied in more cases in both the United States and the United Kingdom. Furthermore, he has been in contact with the U.S. military, which is eager to use the technology for roadside bombs or improvised explosive devices. "Traditional bomb-making metals are ones like copper, which we know corrode with fingerprints," says Bond. "The fingerprint on metal from an exploded bomb should work the same way it does on a bullet with a fingerprint."

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